The Rules of Forgetfulness (Sahw) in Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 50
وَقَالَ اَلصَّادِقُ عَلَيْهِ اَلسَّلاَمُ: «لاَ يَفُوتُ اَلصَّلاَةُ مَنْ أَرَادَ اَلصَّلاَةَ وَ لاَ تَفُوتُ صَلاَةُ اَلنَّهَارِ حَتَّى تَغِيبَ اَلشَّمْسُ وَ لاَ صَلاَةُ اَللَّيْلِ حَتَّى يَطْلُعَ اَلْفَجْرُ.
Imam Jafar ibn Muhammad Al-Sadiq عليه السلام said: "No one misses a prayer who truly desires to pray. The prayer of the day does not miss until the sun sets, and the prayer of the night does not miss until dawn breaks."
- Ṣaḥīḥ al-Faqīh