What are the criteria that determine when one should ask and research issues concerning nullifiers of fasting and prayer, and what is the wisdom behind the jurists not mentioning everything that could nullify an act of worship when enumerating nullifiers?

The majority of scholars hold that rectal suppositories (inserting something into the anus) invalidate the fast, whether it is liquid or solid. The Malikis specified this to liquid substances, while the Shafi'is and Hanbalis consider anything that reaches the interior of the body through the anus as invalidating the fast. The Hanafis consider the disappearance of dry cotton as invalidating the fast.

However, Sheikh al-Islam Ibn Taymiyyah and a group of scholars disagreed, holding that suppositories do not break the fast because they are not considered eating or drinking, neither linguistically nor customarily. Furthermore, there is no legal evidence to suggest that everything that reaches the interior of the body through any orifice invalidates the fast.

Scholars have mentioned that being overly strict in identifying invalidators of the fast is blameworthy and leads to obsessive doubts (waswas), while being overly lenient leads to negligence. The best approach is a middle ground. This can be addressed by reading concise fiqh books. If the questioner is suffering from waswas, they should ignore it or consult a specialized doctor if necessary.