Sahih Muslim Book - 5, Hadith - 1274

وَحَدَّثَنَا عُثْمَانُ وَأَبُو بَكْرٍ ابْنَا أَبِى شَيْبَةَ وَإِسْحَاقُ بْنُ إِبْرَاهِيمَ جَمِيعًا عَنْ جَرِيرٍ - قَالَ عُثْمَانُ حَدَّثَنَا جَرِيرٌ - عَنْ مَنْصُورٍ عَنْ إِبْرَاهِيمَ عَنْ عَلْقَمَةَ قَالَ قَالَ عَبْدُ اللَّهِ صَلَّى رَسُولُ اللَّهِ -صلى الله عليه وسلم- - قَالَ إِبْرَاهِيمُ زَادَ أَوْ نَقَصَ - فَلَمَّا سَلَّمَ قِيلَ لَهُ يَا رَسُولَ اللَّهِ أَحَدَثَ فِى الصَّلاَةِ شَىْءٌ قَالَ « وَمَا ذَاكَ ». قَالُوا صَلَّيْتَ كَذَا وَكَذَا - قَالَ - فَثَنَى رِجْلَيْهِ وَاسْتَقْبَلَ الْقِبْلَةَ فَسَجَدَ سَجْدَتَيْنِ ثُمَّ سَلَّمَ ثُمَّ أَقْبَلَ عَلَيْنَا بِوَجْهِهِ فَقَالَ « إِنَّهُ لَوْ حَدَثَ فِى الصَّلاَةِ شَىْءٌ أَنْبَأْتُكُمْ بِهِ وَلَكِنْ إِنَّمَا أَنَا بَشَرٌ أَنْسَى كَمَا تَنْسَوْنَ فَإِذَا نَسِيتُ فَذَكِّرُونِى وَإِذَا شَكَّ أَحَدُكُمْ فِى صَلاَتِهِ فَلْيَتَحَرَّ الصَّوَابَ فَلْيُتِمَّ عَلَيْهِ ثُمَّ لْيَسْجُدْ سَجْدَتَيْنِ ».

It was narrated that 'Alqamah said: "'Abdullah said: 'The Messenger of Allah (s.a.w) offered Salat'" - Ibrahim said: "and he added or omitted something. - 'When he said the Salam (at the completion of Salat), it was said to him: "O Messenger of Allah , has something new been introduced into the prayer?" He said: "Why is that?" They said: "You did such and such in the prayer." He turned to face the Qiblah, then he prostrated twice and said the Taslim, then he turned to face us and said: "If anything new had been introduced into the prayer I would have told you. But I am human, I forget as you forget. If I forget, then remind me. If one of you is unsure in his prayer, let him work out what is correct and proceed on that basis, then prostrate twice."