حَدَّثَنِي إِسْحَاقُ بْنُ إِبْرَاهِيمَ، سَمِعَ عَبْدَ الْعَزِيزِ بْنَ عَبْدِ الصَّمَدِ، حَدَّثَنَا مَنْصُورٌ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنِ ابْنِ مَسْعُودٍ ـ رضى الله عنه أَنَّ نَبِيَّ اللَّهِ صلى الله عليه وسلم صَلَّى بِهِمْ صَلاَةَ الظُّهْرِ، فَزَادَ أَوْ نَقَصَ مِنْهَا ـ قَالَ مَنْصُورٌ لاَ أَدْرِي إِبْرَاهِيمُ وَهِمَ أَمْ عَلْقَمَةُ ـ قَالَ قِيلَ يَا رَسُولَ اللَّهِ أَقَصُرَتِ الصَّلاَةُ أَمْ نَسِيتَ قَالَ ‏"‏ وَمَا ذَاكَ ‏"‏‏.‏ قَالُوا صَلَّيْتَ كَذَا وَكَذَا‏.‏ قَالَ فَسَجَدَ بِهِمْ سَجْدَتَيْنِ ثُمَّ قَالَ ‏"‏ هَاتَانِ السَّجْدَتَانِ لِمَنْ لاَ يَدْرِي، زَادَ فِي صَلاَتِهِ أَمْ نَقَصَ، فَيَتَحَرَّى الصَّوَابَ، فَيُتِمُّ مَا بَقِيَ، ثُمَّ يَسْجُدُ سَجْدَتَيْنِ ‏"‏‏.‏

Narrated Ibn Mas`ud:that Allah's Prophet led them in the Zuhr prayer and he offered either more or less rak`at, and it was said to him, "O Allah's Messenger (ﷺ) ! Has the prayer been reduced, or have you forgotten?" He asked, "What is that?" They said, "You have prayed so many rak`at." So he performed with them two more prostrations and said, "These two prostrations are to be performed by the person who does not know whether he has prayed more or less (rak`at) in which case he should seek to follow what is right. And then complete the rest (of the prayer) and perform two extra prostrations