Is it permissible to perform ablution by wiping over the upper khuffs if they were worn over another pair of khuffs, given that one does not recall whether he was in a state of purity (wudu') when he put on the upper khuffs, and is he required to repeat (his prayers)?

It is permissible to wipe over the upper khuff (leather slipper) or sock if it was put on after a complete purification and before invalidating the wudu' (ablution). However, if it was put on after invalidating the wudu', it is not permissible to wipe over it, because one of the conditions for wiping is putting it on while in a state of complete purification. So, if a person puts on the upper khuffayn (two leather slippers) and doubts whether he was in a state of wudu' or not, his situation is one of two:

1. He had performed wudu' before that and is not certain of anything that would invalidate the wudu': He is considered to be in a state of wudu', and his wiping over the upper khuff is valid, because certainty is not removed by doubt. 2. He had performed wudu' and something that invalidates it occurred, then he doubted whether he performed wudu' after that: He is considered to be in a state of impurity, because the invalidation is certain, and the wudu' is doubtful. He must repeat the prayers he performed with this invalid wudu'.

This is the view of the majority of scholars. However, Shaykh al-Islam Ibn Taymiyyah was of the opinion that whoever omits a condition or a pillar of prayer out of ignorance is not required to repeat it.