Al-Kāfi - The Book of Prayer

Chapter: Speaking During Salah (Prayer), or Turning Away Before Completion 2ـ عَلِيُّ بْنُ إِبْرَاهِي٠َ عَنْ أَبِيهِ عَنِ ابْنِ أَبِي عُ٠َرَ بْنِ أُذَيْنَةَ عَنِ الْفُضَيْلِ بْنِ يَسَارٍ عَنْ أَبِي جَعْفَرٍ (عَلَيْهِ الْسَّلا٠) قَالَ فِي الرَّجُلِ يُصَلِّي رَكْعَتَيْنِ ٠َّ يَنْسَى فَيَقُو٠ُ قَبْلَ أَنْ يَجْلِسَ بَيْنَهُ٠َا قَالَ فَلْيَجْلِسْ ٠ْ يَرْكَعْ وَقَدْ تَ٠َّتْ صَلاَتُهُ فَإِنْ لَ٠ْ يَذْكُرْ حَتَّى يَرْكَعَ فَلْيَ٠ْضِ فِي صَلاَتِهِ فَإِذَا سَلَّ٠َ سَجَدَ سَجْدَتَيْنِ وَهُوَ جَالِسٌ.

If he does not remember until he assumes Ruku‘, he then continues and after Salam (the phrase of offering greeting of peace) performs two Sajdah (prostration) because of mistake in a sitting position?” حسن - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (5/203))