Must one verify that nothing has emerged from the anus after defecation before each prayer, and is it necessary to repeat past prayers when unaware of their number?

Whoever performs ablution (wudu') remains in a state of purity until he is certain of an impurity (hadath) that invalidates it. His ablution is not invalidated merely by doubt, even if the doubt is strong or conjecture prevails, because the original state is the persistence of purity. Therefore, merely feeling something exiting from the anus does not invalidate ablution, and there is no need to examine after cleansing (istinja'), nor should prayers that have been performed be repeated. This principle is supported by the hadith: "He should not leave [his prayer] until he hears a sound or finds a smell." There is no need for "salt and natr" (squeezing and pulling) after urination; rather, it is sufficient to wash only the head of the penis, and one should ignore obsessive whispers (waswasah).