Praise be to Allah.
After relieving oneself , it is obligatory to remove whatever najasah (impurity) there is in that place, whether it is removed with water or something else, such as stones or paper or tissues , but using water is best.
The scholars of the Standing Committee for Issuing Fatwas were asked: In Britain we use tissues and paper to clean ourselves in the bathroom ; is it obligatory to use water after using tissues, or not?
“All praises belong to Allah Alone, and blessings and peace be upon His Messenger and his family and Companions.
It is permissible to use tissues and papers and the like to clean oneself, and that is sufficient if it is done properly and the place is cleaned, from front or back. But it is better if what is used for cleaning is odd-numbered, and it should not be less than three wipes. It is not essential to use water after that, but it is Sunnah. May Allah send blessings and peace upon our Prophet Muhammad.”
Shaykh ‘Abd al-‘Aziz ibn ‘Abd-Allah ibn Baz, Shaykh ‘Abd al-Razzaq ‘Afifi, Shaykh ‘Abd-Allah ibn Ghadyyan, Shaykh ‘Abd-Allah ibn Qa’ud.” (Fatawa al-Lajnah al-Daimah, 5/125)
Shaykh Muhammad al-Salih al-‘Uthaymin (may Allah have mercy on him) was asked: It is acceptable to use tissues to clean oneself after defecating?
“Yes, it is sufficient to use tissues to clean oneself after defecating, and there is nothing wrong with it, because the purpose of cleaning oneself is to remove the impurity, whether it is done with tissues, cloth, dust or stones. But it is not permissible for a person to clean himself with things that are forbidden in shari’ah, such as bones and dung, because bones are the food of the jinn, if they are from animals that were slaughtered properly; if they are from animals that were not slaughtered properly, then they are najis (impure), and that which is impure cannot purify. As for dung, if it is najis then it cannot purify, and if it is tahir (pure), then it is food for the animals of the jinn, because when the jinn came to the Prophet (peace and blessings of Allah be upon him) and believed in him, he gave them some food which will not stop until the Day of Resurrection. He said to them: “For you is every bone on which the name of Allah is mentioned, and you will find it with plenty of meat on it.” This is one of the matters of the unseen that we cannot see, but we are obliged to believe in it. Similarly, dung is food for their animals.” (Majmu’ Fatawa Ibn ‘Uthaymin, 4/112)
And Allah knows best.