What is the ruling according to the Shafi'i school on replacing water with tissue for Istinja' for someone afflicted with Waswas (obsessive doubts), when urine or feces have exited in an amount exceeding a dirham? And is ghusl (washing) with water obligatory when it is available?

We ask Allah to grant you healing from obsessive thoughts, and we advise you to disregard them. Regarding the Shafi'i school of thought, it is sufficient for you to perform istinjā’ by wiping the place of urination or defecation three times until complete purification is achieved, such that nothing remains except a trace that cannot be removed except by water. You are not obligated to use water at all in this case. Al-Shirazi and Al-Nawawi state that three wipes are obligatory along with the removal of the substance itself, and that the ruling for men and women regarding the istinjā’ of the anus is the same. It is permissible for a woman to suffice with a stone.