Answered by Ustadh Sufyan Qufi
Sometimes, I think I become impure after passing a lot of wind. When I take a tissue and wipe my behind in these instances, the tissue has some brown on it.
My question is, do I have to istinja’ in this case?
In the name of Allah, Most Compassionate, Most Merciful,
The small amount of filth exiting the body after passing a wind does not need to be removed in order to pray a valid prayer.
The air exiting the body while passing wind is pure, according to the Hanafi school. Thus performing istinja’ after passing wind is a blameworthy innovation. [Shurunbulali, Maraqi al-Falah]
More Details on the Rulings of Istinja’
It is an emphasized sunna to remove filth from the rear area (point of exit) as long as it doesn’t go beyond the rear area, which is roughly a circle of 5 cm diameter around the point of exit. This removal is called istinja’.
Not performing istinja, in this case won’t prevent the validity of the prayer. [Shurunbulali, Maraqi al-Falah; Shurunbulali, Ascent to Felicity]
If the filth covers the rear area and beyond, it becomes necessary (wajib) to remove it with water.
If not performed, the prayer will still be valid as long as the filth spread beyond the rear area is not as large as the rear area (ie, a circle of 5 cm diameter).
It would be highly farfetched to have such an amount of filth exit the body after passing a wind. Rather you can assume that the hypothetical filth outside of the body after a wind will never go past the rear area.
Allah Most High says: “Allah intends (to provide) ease for you and does not intend (to create) hardship for you.” [Quran, 2:185]
If you are sure there is filth in this area after passing wind, then it remains an emphasized sunna to remove it. But failing to do so won’t affect the validity of your prayer.
And Allah knows best.
[Ustadh] Sufyan Qufi
Checked and Approved by Shaykh Faraz Rabbani