Question 036: If one gets Doubts (shakk) during the salah that wudu was not taken, should one break the salah to perform wudu?
Answer 036: If a person doubts during prayer (namaz) whether he has performed wuhu or not, his prayers is void, and he must perform wudhu and then pray. If a person is sure that he has performed wudu but doubts whether he has committed an act which invalidates it or not his wudu would be considered as valid.
If a person doubts whether his Wudhu has become void, he should treat it as valid. But, if he did not perform Istibra after urinating, and performed Wudhu, and thereafter some fluid was discharged about which he was not sure whether it was urine or something else, his Wudhu will be void.
If a person doubts whether he has performed Wudhu or not, he should perform Wudhu.
If a person is sure that he has performed Wudhu, and has also committed an act which invalidates Wudhu (e.g. urinating), but does not remember which happened first, he should act as follows: If this situation arises before his Namaz, he should perform Wudhu. If it arises during Namaz, he should break it and perform Wudhu. If it arises after Namaz, that Namaz will be valid, but for the next prayers, however, he should perform Wudhu.[1]
[1]. Tawzih al-Masael of maraja (with annotation), Sayyid Roohullah al-Moosavi al-Khomeini, Vol. 1, Pg. 179, question 301, eighth edition, 1424 A.H. http://www.sistani.org/english/book/48/2157/; The Official Website of the Office of Sayyid Sistani, Rules regarding Wudhu.