Purity: Cases Requiring Water for Purification of the Back Passage
Practical Laws of Islam as per the teaching of Ayatullah Sistani
Ruling 61
In three cases, the anus can be purified with water only:[6]1
1. another impurity like blood comes out with the faeces;
2. an external impurity comes into contact with the anus, except if urine comes into contact with the anus in the case of women;
3. if the area around the anus has become impure by an amount that is more than usual.
In cases other than these three, the anus can be purified with water, or, in accordance with the instructions that will be mentioned later, it can be purified with cloth, stone, or a similar thing, although it is better to wash it with water.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)
[6] Rulings 61–68 concern a matter that is referred to in Islamic law as ‘istinjāʾ’, i.e. purification of the anus and the urinary outlet.