Chapter on the Rulings on Forgetfulness (Ahkam al-Sahw)
Tahdhīb al-Aḥkām|Volume 2|Book 1|Chapter 16
اَلْحُسَيْنُ بْنُ سَعِيدٍ عَنْ فَضَالَةَ عَنْ أَبِي اَلْمَغْرَاءِ قَالَ: سَأَلْتُ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ عَنِ اَلرَّجُلِ يَكُونُ خَلْفَ اَلْإِمَامِ فَيَسْهُو فَيُسَلِّمُ قَبْلَ أَنْ يُسَلِّمَ اَلْإِمَامُ قَالَ« لاَ بَأْسَ»
Al-Husayn ibn Sa‘id from Faddalah from Abu al-Maghra, who said:
I asked Abu Abdillah عليه السلام, peace be upon him, about a man who is behind the Imam (of prayer) and, due to forgetfulness, gives salam before the Imam (of prayer) does. Imam عليه السلام said: "There is no harm."
- Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 375
- Ṣaḥīḥ al-Tahdhīb, p. 232