Sunan Abi Dawud 1024
سنن أبي داود#1024Sahih‘Ata’ b. Yasar said that Abu Sa’id al-Khudri reported the Messenger of Allah (ﷺ) as saying:when one of you is in doubt about his prayer (i.e, how much he has prayed), he should throw away his doubt and base his prayer on what he is sure of. When he is sure about the completion of his prayer, he should make two prostrations (at the end of the prayer). If the prayer is complete, the additional rak’ah and the two prostrations will be supererogatory prayer. If the prayer is incomplete, the additional rak’ahs will compensate it, and the two prostrations will be a disgrace for the devil
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniHasan Sahih
Muhammad Muhyi Al-Din Abdul HamidHasan Sahih
Zubair Ali ZaiSahih Muslim (571)
In-book reference: 2:635