What is the ruling on the remains of impurity from feces or urine on clothes?

Impurity present on clothes must be removed in all cases. Previous prayers do not need to be repeated if the worshiper was unaware of the impurity's presence. If the impurity resulted from something exiting one of the two passages without feeling it, then the impurity must be removed and ablution performed for prayer. Whoever prays and then sees impurity but is unaware of when it was present (before or after the prayer), their prayer is valid and they do not need to repeat it.