مُسْنَدُ عُثْمَانَ بْنِ عَفَّانَ رَضِيَ اللَّهُ عَنْهُ
4  
Musnad Uthman ibn Affan
Musnad Ahmad 450, 451
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.

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ الزُّبَيْرِ، حَدَّثَنَا مَسَرَّةُ بْنُ مَعْبَدٍ، عَنْ يَزِيدَ بْنِ أَبِي كَبْشَةَ، عَنْ عُثْمَانَ بْنِ عَفَّانَ، رَضِيَ اللَّهُ عَنْهُ قَالَ جَاءَ رَجُلٌ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ يَا رَسُولَ اللَّهِ إِنِّي صَلَّيْتُ فَلَمْ أَدْرِ أَشَفَعْتُ أَمْ أَوْتَرْتُ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِيَّايَ وَأَنْ يَتَلَعَّبَ بِكُمْ الشَّيْطَانُ فِي صَلَاتِكُمْ مَنْ صَلَّى مِنْكُمْ فَلَمْ يَدْرِ أَشَفَعَ أَوْ أَوْتَرَ فَلْيَسْجُدْ سَجْدَتَيْنِ فَإِنَّهُمَا تَمَامُ صَلَاتِهِ.

حَدَّثَنَا يَحْيَى بْنُ مَعِينٍ وَزِيَادُ بْنُ أَيُّوبَ قَالَا حَدَّثَنَا سَوَّارٌ أَبُو عُمَارَةَ الرَّمْلِيُّ عَنْ مَسِيرَةَ بْنِ مَعْبَدٍ قَالَ صَلَّى بِنَا يَزِيدُ بْنُ أَبِي كَبْشَةَ الْعَصْرَ فَانْصَرَفَ إِلَيْنَا بَعْدَ صَلَاتِهِ فَقَالَ إِنِّي صَلَّيْتُ مَعَ مَرْوَانَ بْنِ الْحَكَمِ فَسَجَدَ مِثْلَ هَاتَيْنِ السَّجْدَتَيْنِ ثُمَّ انْصَرَفَ إِلَيْنَا فَأَعْلَمَنَا أَنَّهُ صَلَّى مَعَ عُثْمَانَ رَضِيَ اللَّهُ عَنْهُ وَحَدَّثَ عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَذَكَرَ مِثْلَهُ نَحْوَهُ‏.‏

Grade: Hasan and its isnad is da'eef because it is interrupted] lts isnad is Hasan] (Darussalam)
Reference : Musnad Ahmad 450, 451
In-book reference : Book 4, Hadith 46