Doubting Wudu' after performing it

Q 8: If I doubt whether I have performed Wudu' (ablution) or not, does this invalidate my Wudu'? Also, if I doubt whether I have offered Zhuhr (Noon) Prayer or not, should I offer Zhuhr (Noon) Prayer to clear my doubts or ignore the doubts and do what I am certain of? If I realize that I was wrong in guessing the direction of the Qiblah (Ka`bah-direction faced in Prayer), should I repeat my Salah (Prayer)? (Part No. 4; Page No. 122

A: First: If a person performs Wudu' then doubts whether he has become ritually impure or not, the rule is that he continues to be in a state of Wudu' until he is sure that he has passed into a state of Hadath (ritual impurity that invalidates ablution). Thus, he should build upon the main state and disregard doubts.On the other hand, if a person has not performed Wudu' then doubts whether has performed Wudu' or not, the rule is that he has not performed Wudu' unless there is proof that makes him certain of having performed Wudu'. Thus, he should build upon the main state, i.e. not performing Wudu'.The rule of Shari`ah (Islamic law) in this regard is that certainty is not removed by doubt. The basic ruling is continuity of a certain state until there is proof of it being cancelled.Second: If a person doubts whether he has performed Salah or not, the rule is that he has not offered it until he is certain of having offered it.Third: If a person does not find anyone to tell him about the direction of the Qiblah, and cannot find it on his own, and makes an effort to guess it, then offers Salah, then later on finds out that he is wrong in his guess, this person does not have to repeat Salah and his Salah is valid, all praise be to Allah.But if this person ignores asking people about it or checking to know it, then finds out that he has been wrong in his guess, his Salah is not valid and he has to repeat it.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.