The Rules of Forgetfulness (Sahw) in Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 50
وَ رَوَى اَلْحَسَنُ بْنُ مَحْبُوبٍ عَنِ اَلرِّبَاطِيِّ عَنْ سَعِيدٍ اَلْأَعْرَجِ قَالَ سَمِعْتُ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ يَقُولُ: «إِنَّ اَللَّهَ تَبَارَكَ وتَعَالَى أَنَامَ رَسُولَهُ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ، عَنْ صَلاَةِ اَلْفَجْرِ حَتَّى طَلَعَتِ اَلشَّمْسُ ثُمَّ قَامَ فَبَدَأَ فَصَلَّى اَلرَّكْعَتَيْنِ اَللَّتَيْنِ قَبْلَ اَلْفَجْرِ ثُمَّ صَلَّى اَلْفَجْرَ وَ أَسْهَاهُ فِي صَلاَتِهِ فَسَلَّمَ فِي رَكْعَتَيْنِ ثُمَّ وَصَفَ مَا قَالَهُ ذُو اَلشِّمَالَيْنِ وَ إِنَّمَا فَعَلَ ذَلِكَ بِهِ رَحْمَةً لِهَذِهِ اَلْأُمَّةِ لِئَلاَّ يُعَيَّرَ اَلرَّجُلُ اَلْمُسْلِمُ إِذَا هُوَ نَامَ عَنْ صَلاَتِهِ أَوْ سَهَا فِيهَا فَيُقَالُ قَدْ أَصَابَ ذَلِكَ رَسُولَ اَللَّهِ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ.
Al-Hasan ibn Mahbub narrated from Al-Rabati, from Saeed Al-A'raj who said: "I heard Abu Abdullah عليه السلام (Imam Ja'far Al-Sadiq عليه السلام) say: 'Indeed, Allah سبحانه وتعالى, the Blessed and Exalted, caused His Messenger صلى الله عليه وعلى آله وسلم to sleep through the Fajr prayer until the sun had risen. Then he stood up and prayed the two rak'ahs before Fajr, followed by the Fajr prayer. He forgot during his prayer, so he made a mistake and gave the salutation in two rak'ahs. Then he described what Dhul-Shimālayn (who pointed out the mistake) said. He did this out of mercy for this ummah, so that no Muslim man would be reproached if he sleeps through his prayer or makes a mistake in it, and so that it would be said: 'This happened to the Messenger of Allah صلى الله عليه وعلى آله وسلم.'".
- Ṣaḥīḥ al-Faqīh