صحيح ابن خزيمه
Sahih Ibn Khuzaymah
جماع أبواب السهو فى الصلاةChapters on Forgetfulness in Prayer
(430) بَابُ ذِكْرِ الْبَيَانِ أَنَّ الْمُصَلِّيَ إِذَا قَامَ مِنَ الثِّنْتَيْنِ فَاسْتَوَى قَائِمًا،The chapter clarifying that if one stands up after two units and becomes fully upright
Hadith Q1031
ثُمَّ ذُكِّرَ بِتَسْبِيحٍ أَنَّهُ نَاسٍ لِلْجُلُوسِ، أَنَّ عَلَيْهِ الْمُضِيَّ فِي صَلَاتِهِ، تَرْكَ الرُّكُوعِ إِلَى الْجُلُوسِ، وَعَلَيْهِ سَجْدَتَا السَّهْوِ قَبْلَ السَّلَامِ
Then he should be alerted by saying "Subhanallah" that he forgot to sit for Tashahhud, so he should continue his prayer and, after standing up, should not sit down again, and before saying the Salam, he should perform two prostrations.
