Sunan an-Nasa'i 1245
سنن النسائي#1245SahihIt was narrated that 'Abdullah said:"Whoever us not sure about his prayer, then let him estimate what is correct, then let him prostrate twice after he finished his prayer, while he is sitting
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 13:67