Sunan Ibn Majah 1204
سنن ابن ماجه#1204Sahih‘Iyad narrated that he asked Abu Sa’eed Al-Khudri:“One of us prays and he does not know how many (Rak’ah) he has prayed.” He said: “The Messenger of Allah (ﷺ) said: ‘When anyone of you prays and does not know how many he has prayed, let him perform two prostrations while he is sitting.’”
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Zubair Ali ZaiIsnaad Hasan
In-book reference: 5:402