Praise be to Allah.
Firstly: discussion of what is meant by “an eye that stays awake, guarding in the cause of Allah”
At-Tirmidhi (1639) narrated that Ibn ‘Abbaas said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “There are two eyes that the Fire will not touch: an eye that weeps out of fear of Allah, and an eye that stays awake, guarding in the cause of Allah.” Classed as saheeh by al-Albaani in Saheeh at-Tirmidhi.
It was narrated by al-Haakim in al-Mustadrak (2431) that Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “It is forbidden for the Fire to touch two eyes: an eye that weeps out of fear of Allah, and an eye that stays awake, guarding Islam and its people from the disbelievers.” Al-Albaani said in Saheeh at-Targheeb wa't-Tarheeb (1233): It is saheeh because of corroborating evidence.
What is meant by guarding is guarding the border (muraabatah) in the case of jihad (i.e., a military scenario).
It says in Daleel al-Faaliheen (7/106): This includes anyone who guards the army against the enemy, and guards border posts (ribaat). End quote.
It says in Mirqaat al-Mafaateeh (62479): “An eye that stays awake, guarding – according to another report: keeping watch – in the cause of Allah”: this is the level of the mujaahideen that one may attain when doing an act of worship. This includes when going for Hajj, seeking knowledge, engaging in jihad, or engaging in worship. But the most likely meaning is the one who guards other mujaahideen to protect them from the disbelievers. End quote.
We have not come across anyone who regards the doctor on call as being included in this. Rather they mention hajj and seeking knowledge because these two scenarios may be described as being in the cause of Allah.
Secondly: medicine is one of the noblest branches of knowledge after Islamic (shar‘i) knowledge
Medicine is one of the noblest branches of knowledge after Islamic (shar‘i) knowledge, because of what it involves of maintaining physical well-being.
Imam Ibn Abi Haatim ar-Raazi narrated in Aadaab ash-Shaafa‘i wa Manaaqibuhu (p. 244) that ar-Rabee‘ ibn Sulaymaan said: I heard ash-Shaafa‘i say: Knowledge is of two types: religious knowledge and worldly knowledge. Religious knowledge is fiqh (and learning about Islamic teachings) and worldly knowledge is medicine. Everything else, such as poetry and the like, is a waste of effort or something shameful.
And it was narrated from him that he said: Never live in a city where there is no scholar who could answer your questions about religious matters and no doctor who could advise you about your physical well-being. End quote.
In his biography of ash-Shafa‘i in Siyar A‘laam an-Nubala’, adh-Dhahabi quoted him as saying: I do not know of any branch of knowledge, after knowledge of what is halaal and haraam, that is nobler than medicine, but the People of the Book have overtaken us in that field.
Harmalah said: ash-Shaafa‘i used to feel very sad about the Muslims’ lack of interest in medicine, and he would say: They have neglected one third of knowledge and left it to the Jews and Christians. End quote.
If a doctor has good intentions, he will be rewarded greatly, because his work comes under the heading of showing kindness to others, relieving distress, and benefitting people, whilst doing good and showing generosity.
Allah, may He be exalted, says (interpretation of the meaning):
“and Allah loves the doers of good”
[Aal ‘Imraan 3:134]
“Is the reward for good [anything] but good”
The Prophet (blessings and peace of Allah be upon him) said: “Whoever removes a hardship from a believer in this world, Allah will remove one of the hardships of the Day of Resurrection from him. Whoever grants respite to (a debtor) who is in difficulty, Allah will grant him relief in this world and in the Hereafter. Whoever conceals (the fault of) a Muslim in this world, Allah will conceal him (his faults) in this world and in the Hereafter. Allah will help a person so long as he is helping his brother. Whoever follows a path seeking knowledge, Allah will make a path to Paradise easy for him. No people gather in one of the houses of Allah, reciting the Book of Allah and studying it together, but tranquillity will descend upon them, mercy will overshadow them, the angels will surround them and Allah will mention them to those who are with Him. Whoever is slowed down by his deeds, his lineage will not help him to get ahead.” Narrated by Muslim.
And he (blessings and peace of Allah be upon him) said: “The most beloved of people to Allah, may He be exalted) is the one who is most helpful to his dependents.” Narrated by ‘Abdullah ibn Ahmad in Zawaa’id az-Zuhd; classed as hasan by al-Albaani in Saheeh al-Jaami‘.
And he (blessings and peace of Allah be upon him) said: “The most beloved of people to Allah is the one who is most helpful to people, and the most beloved of deeds to Allah, may He be glorified and exalted, is bringing joy to a Muslim, relieving him of distress, paying off his debts or warding off his hunger. To walk with a brother of mine to meet his need is dearer to me than observing i‘tikaaf in this mosque – meaning the mosque of Madinah – for a month. And whoever suppresses his anger – even though he could express it if he wanted to – Allah will fill his heart with contentment and pleasure on the Day of Resurrection. Whoever walks with his brother to meet his need and fulfils it, Allah will make his feet steadfast on the Day when feet will slip.” Narrated by Ibn Abi’d-Dunya in Qadaa’ al-Hawaa’ij; classed as hasan by al-Albaani in Saheeh al-Jaami‘.
So seek reward with Allah for what you are doing, and make your intention sincerely in the cause of Allah, hoping for reward from Him, may He be glorified, for you are in the noblest of professions and the best of jobs. Do not forget your portion of different kinds of acts of worship, dhikr and reading Qur’an, for that is your provision for your journey towards the Lord of the Worlds.
And Allah knows best.