Doubt in Mustahab prayers
1202. If a person doubts about the number of Rak'ats in a Mustahab prayer and if the higher side makes the prayers void, he should decide on the lesser side of the doubt. For example, if he doubts whether he has performed 2 Rak'ats or 3 in Nafilah of Fajr prayers, he should decide that he has performed 2 Rak'ats. But if the higher side does not invalidate the prayers, like, if he doubts whether he has performed 2 Rak'ats or 1, he is free to decide either way, and his prayers will be valid.
1203. Omission of a Rukn invalidates Nafilah (Mustahab prayers), but addition of a Rukn does not invalidate it. Hence, if the person offering Nafilah prayers forgets to perform any part, and remembers when he has entered into another Rukn, he should return to perform the forgotten part and then re-enter the Rukn. For example, if he remembers during Ruku that he has not recited Surah al-Hamd, he should return to recite Surah al-Hamd, and then go into Ruku again.
1204. If a person doubts whether he has performed any Rukn or non-Rukn part of Nafilah prayers, he should perform it if its stage has not passed, and if it has, then he should ignore the doubt.
1205. If in a Mustahab prayer of two Rak'ats, a person suspects that he has offered 3 Rak'ats or more, he should ignore his doubt, and his prayers are in order. If, he suspects that he has offered 2 Rak'ats or less, then as an obligatory precaution, he should pay heed to that suspicion. For example, if he suspects that he has performed one Rak'at only, as a precaution, he will perform another Rak'at.
1206. If a person in Nafilah prayers performs an act which, if he had performed in an obligatory prayers, it would have been necessary for him to do Sajdatus Sahv, or if he forgets one Sajdah, it will not be necessary to perform Sajdatus Sahv, or give qadha for the Sajdah, after the Nafilah is over.
1207. If a person doubts whether he has offered a particular Mustahab prayer or not, and if that prayer does not have a fixed time, like, the prayers of Ja'far Tayyar, he should decide that he has not offered it. The position is the same if that prayer has a fixed time, like Nafilah of daily prayers, and a person doubts before its time lapses, whether he has offered it or not. However, if he doubts after its time has gone, he should ignore his doubt.