It was narrated that `Uthman bin `Affan (رضي الله عنه) said: A man came to the Prophet (ﷺ) and said: O Messenger of Allah (ﷺ), I prayed but I do not know whether I did an even number [of rak`ahs] or an odd number. The Messenger of Allah (ﷺ) said: `Beware lest the Shaitan toy with you in your prayer. Whoever among you prays and does not know whether he did an even number [of rak`ahs] or an odd number, let him prostrate twice, for that will complete his prayer.` It was narrated that Masarrah bin Ma`bad said: Yazeed bin Abi Kabshah led us in praying `Asr, then he turned to us after the prayer and said: I prayed with Marwan bin al-Hakam and he did two prostrations like these, then he turned to us and told us that he prayed with ‘Uthman (رضي الله عنه), who narrated from the Prophet (ﷺ) ... and he mentioned a similar report.
Musnad Ahmad, 450, 451Hasan and its isnad is da'eef because it is interrupted] lts
