The Rules of Forgetfulness (Sahw) in Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 50
وَقَالَ أَبُو عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ لِعَمَّارِ بْنِ مُوسَى: «يَا عَمَّارُ أَجْمَعُ لَكَ اَلسَّهْوَ كُلَّهُ فِي كَلِمَتَيْنِ مَتَى مَا شَكَكْتَ فَخُذْ بِالْأَكْثَرِ فَإِذَا سَلَّمْتَ فَأَتِمَّ مَا ظَنَنْتَ أَنَّكَ قَدْ نَقَصْتَ.
Imam Jafar ibn Muhammad Al-Sadiq عليه السلام said to Ammar ibn Musa: "O’ Ammar, I will sum up all forgetfulness for you in two words: Whenever you are in doubt, follow the majority (the greater number). When you finish your prayer, complete what you thought you may have missed”.
- Ṣaḥīḥ al-Faqīh