Praise be to Allah.
One of the most important rights that a wife has is that her husband should spend on her, and his spending on her is one of the greatest good deeds that he can do that will bring him closer to Allaah. This spending covers food, drink, clothing and housing, and all the other things that a wife needs for her sustenance and good health.
With regard to what you mention of your wifes complaints that you are not spending enough on her, Allaah tells us that men are the ones who should spend on women, and they have been given the position of qawwaamah (protector and maintainer) and excellence because of the money they spend on them in the mahr and on their maintenance. Allaah says (interpretation of the meaning): Men are the protectors and maintainers of women, because Allaah has made one of them to excel the other, and because they spend (to support them) from their means [al-Nisa 4:34]. The Quraan, Sunnah and consensus of the scholars (ijmaa) all indicate that this spending is obligatory.
The Quraan tells us (interpretation of the meanings):
the father of the child shall bear the cost of the mothers food and clothing on a reasonable basis. No person shall have a burden laid on him greater than he can bear [al-Baqarah 2:233]
And if they are pregnant, then spend on them till they deliver [al-Talaaq 65:6]
With regard to the evidence of the Sunnah, many ahaadeeth have been narrated which indicate that it is obligatory for a husband to spend on his wife and children and those under his guardianship, as was proven in the hadeeth of Jaabir ibn Abd-Allaah (may Allaah be pleased with him), who reported that the Prophet (peace and blessings of Allaah be upon him) said in his Farewell Sermon: Fear Allaah with regard to women, for they are your prisoners. You have taken them as a trust from Allaah, and they have become permissible to you by the word of Allaah, and they have the right to be fed and clothed reasonably by you.
(Reported by Muslim, 8/183).
Umar ibn al-Ahwas (may Allaah be pleased with him) reported that he heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say during the Farewell Pilgrimage: Take good care of women, for they are your prisoners and you have no rights over them beyond that, except if they commit open illegal lewdness; if they do that, then you should shun them in their beds and strike them, but not in a way that causes pain. And if they return to obedience, seek not against them means (of annoyance). You have rights over your women and your women have rights over you. Your rights over your women are that they should not allow anyone to sit on your beds whom you dislike, or allow anyone to enter your houses who you dislike, and their rights over you are that you should clothe and feed them properly.
(Reported by al-Tirmidhi, 1163; Ibn Maajah, 1851. Al-Tirmidhi said this is a hasan saheeh hadeeth).
Muaawiyah ibn Haydah (may Allaah be pleased with him) said: I said, O Messenger of Allaah, what is the right of the wife of any one of us over us? He said: That you should feed her as you feed yourself and clothe her as you clothe yourself, that you should not say to her May Allaah make your face ugly! and that you should not beat her.
(Reported by Abu Dawood, 2/244; Ibn Maajah, 1850; Ahmad, 4/446).
Imaam al-Baghawi said: Al-Khattaabi said: This means that it is obligatory to spend on her and clothe her, according to the means of the husband. Because the Prophet (peace and blessings of Allah be upon him) made it a right of the wife, it is obligatory on the husband whether he is present or absent. If he is not able to do this at any particular time, it becomes a debt that he owes, as in the case of other duties, whether or not the qaadi (judge) imposes it on him for the time when he is absent.
Wahb said: A freed slave of Abd-Allaah ibn Amr said to him: I want to spend this month here in Bayt al-Maqdis (Jerusalem). He said, Have you left your family anything for their provisions during this month? He said, No. He said, Then go back to your family and leave them something for their provisions, for I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) saying, It is enough sin for a man to neglect those he is responsible to feed.
(Reported by Ahmad, 2/160; Abu Dawood, 1692)
The original hadeeth is reported by Muslim (245), with the wording: It is enough sin for a man to keep food away from those he is responsible to feed.
Anas (may Allaah be pleased with him) reported that the Prophet (peace and blessings of Allaah be upon him) said: Allaah will ask every responsible person (literally, shepherd) about those for whom he was responsible, whether he took care of them or not, and He will even ask a man about the members of his household.
(Reported by Ibn Hibbaan and classed as hasan in Saheeh al-Jaami, 1774).
Abu Hurayrah (may Allaah be pleased with him) said: I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say: By Allaah, if one of you were to go out in the morning and gather firewood on his back, and sell it and make himself independent, and give some of it in charity, this is better for him than his coming to a man and asking for anything, whether he gives or refuses. The upper hand is better than the lower hand, and start with those who are under your care.
(Reported by Muslim, 3/96). According to a report narrated by Ahmad (2/524): It was said, Who are those who are under our care, O Messenger of Allaah? He said, Your wife is one of those who are under your care.
With regard to the consensus of the scholars (ijmaa):
Imaam Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni (7/564): The scholars are agreed that it is obligatory on men to spend on their wives, except in the case of a wife who is rebellious. This was mentioned by Ibn al-Mundhir and others.
The texts referred to above indicate that it is obligatory for a man to spend on his household and to take care of them and their best interests. Numerous ahaadeeth reported from the Prophet (peace and blessings of Allaah be upon him) describe the virtue of this and state that it is a righteous deed in the sight of Allaah, for example the hadeeth of Abu Masood al-Ansaari (may Allaah be pleased with him), according to which the Prophet (peace and blessings of Allaah be upon him) said: If a Muslim spends on his wife, and hopes for reward from Allaah, it will be counted as sadaqah (charity) on his part.
(Reported by al-Bukhaari, 1/136).
Al-Haafiz ibn Hajar (may Allaah have mercy on him) said in al-Fath (9/498): Spending on ones wife is obligatory according to consensus (ijmaa), and Islam described it as charity lest people think that it is only a duty for which they will not be rewarded, for they already know the rewards for charity. Islam taught them that it will be counted as charity so that they will not give to others besides their wives until they (the wives) have enough, to encourage them to give obligatory charity before they give voluntary charity.
Sad ibn Maalik (may Allaah be pleased with him) reported that the Prophet (peace and blessings of Allaah be upon him) said to him: No matter what you spend on your family, you will be rewarded, even for the morsel of food you put in your wifes mouth.
(Reported by al-Bukhaari, 3/164, and Muslim, 1628).
Abu Hurayrah (may Allaah be pleased with him) reported that the Prophet (peace and blessings of Allaah be upon him) said: A dinar spent for the sake of Allaah, a dinar spent to free a slave, a dinar given in charity to a poor person, and a dinar spent on ones wife the greatest in reward of all these is the dinar spent on one's wife.
(Reported by Muslim, 2/692)
Kab ibn Ijrah (may Allaah be pleased with him) said: A man passed by the Prophet (peace and blessings of Allaah be upon him), and his Companions were impressed with how strong and energetic he appeared. They said, O Messenger of Allaah, if only this was for the sake of Allaah! The Messenger of Allaah (peace and blessings of Allaah be upon him) said: If he is going out to earn a living for his young children, this is for the sake of Allaah; if he is going out to earn a living for his aged parents, this is for the sake of Allaah; if he is going out to earn a living so he can keep himself from begging from others, this is for the sake of Allaah; but if he is going out to boast and show off, then this is for the sake of Shaytaan.
(Reported by al-Tabaraani, Saheeh al-Jaami, 2/8)
The salaf (may Allaah have mercy on them) understood this duty properly, and said words to that effect. How marvellous are the words of the great imaam Abd-Allaah ibn al-Mubaarak (may Allaah have mercy on him): There is nothing equivalent in reward to earning money to spend on your family, not even jihaad for the sake of Allaah.
At the same time, your wife should understand that the husbands obligation to spend should be within his means and according to his financial situation, as Allaah says (interpretation of the meaning): Let the rich man spend according to his means, and the man whose resources are restricted, let him spend according to what Allaah has given him. Allaah puts no burden on any person beyond what He has given him. Allaah will grant after hardship, ease. [al-Talaaq 65:7]
She has no right to mistreat her husband by asking him for too much and expecting him to exhaust himself in spending on her; that is bad treatment indeed. Perhaps if you grant her some of her reasonable requests and remind her, gently and tactfully, of the requests that you have fulfilled, you may be able to lessen her anger somewhat and persuade her to stop asking for more. You could also discuss with her, quietly and without resorting to arguing, how important her requests really are and how necessary it is to keep a certain amount for things that are more important, like paying the rent and so on. This may also persuade her to stop asking.
Know that what you lack in financial resources can be compensated for with kind words and promises for when things get better. When Allaah mentioned taking care of ones relatives and upholding family ties, He also mentioned what a person can do who does not have money to give to his relatives. He says (interpretation of the meaning): And if you turn away from them (relatives, the poor etc. whom We have ordered you to give their rights, but you have no money at the time they ask for it) and you are awaiting a mercy from your Lord for which you hope, then speak unto them a kind, soft word (i.e., Allaah will give me and I shall give you). [al-Isra 18:28]
Ibn Katheer (may Allaah have mercy on him) said in his interpretation of this aayah: And if you turn away from them (relatives, the poor etc. whom We have ordered you to give their rights, but you have no money at the time they ask for it) and you are awaiting a mercy from your Lord for which you hope means: if your relatives ask you for something that We have commanded you to give them, and you do not have anything, and you turn away from them because you have nothing to spend on them, then speak unto them a kind, soft word which means, promise them, gently and kindly, that when the provision of Allaah comes, we will give it to you, in sha Allaah.
Know that a good attitude will make her forget the hardship you are going through. You have to be patient and treat her kindly, whilst repeating your advice. If life becomes too difficult and the situation between you deteriorates to such an extent that you reach a total impasse, if your efforts do not succeed and life becomes unbearable, then Allaah has permitted divorce in such cases, and this may indeed be better for both parties, as He says (interpretation of the meaning): But if they separate (by divorce), Allaah will provide abundance for everyone of them from His Bounty. And Allaah is Ever All-Sufficient for His creatures need, All-Wise. [al-Nisa 4:130]