Liaison office of Grand Ayatullah Sayyid Ali Al Sistani (L.M.H.L) in London, Europe, North and South America.
1188. If a person becomes doubtful after the Salam of prayers, as to
whether or not he has offered the prayers correctly, like, if he doubts whether
or not he has performed the Ruku, or doubts in a 4 Rak'at prayers as to whether
he has performed 4 or 5 Rak'ats, he should ignore his doubt. But if both sides
of the doubt lead to invalidity of the prayers like, if he doubts in 4 Rak'at
prayers whether he has performed 3 or 5 Raka'ts, his prayers would be
void.