The Prophet (ﷺ) named the two prostrations of forgetfulness disgraceful for the devil.
Sunan Abi Dawud Book 2, Hadith 636
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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.
Sunan Abi Dawud Book 2, Hadith 635 Next Hadith → The Prophet (ﷺ) said: When one of you is in doubt about his prayer, and does not know how much he has prayed, three or four rak'ahs, he should pray one (additional) rak'ah and make two prostrations while sitting before giving the salutation. If the (additional) rak'ah which he prayed is the fifth one, he will make it an even number by these two prostrations. If it is the fourth one, the two prostrations will be a disgrace for the devil.
Sunan Abi Dawud Book 2, Hadith 637
Sunan Abi Dawud Book 2, Hadith 635 Next Hadith → The Prophet (ﷺ) said: When one of you is in doubt about his prayer, and does not know how much he has prayed, three or four rak'ahs, he should pray one (additional) rak'ah and make two prostrations while sitting before giving the salutation. If the (additional) rak'ah which he prayed is the fifth one, he will make it an even number by these two prostrations. If it is the fourth one, the two prostrations will be a disgrace for the devil.
Sunan Abi Dawud Book 2, Hadith 637