I said to him: the one who does not know whether he is in the fourth or the second (Rak’a) but is sure that he has completed two [what should he do]? He said: he will perform two units and four prostrations and he stands reciting al-Fatiha and makes the Tashahud, and there is nothing further upon him, and if he does not know whether he is in the third or the fourth but he is sure that he has completed three – he stands and adds another (unit) to them and there is nothing further upon him. Certainty is not overriden by doubt and doubt does not enter certainty, one of them does not mix with the other, rather doubt is overriden by certainty, and one completes upon certainty building upon it, and doubt is regarded in any situation whatsoever.