From Sahih Bukhari (Hadith 1232):
Narrated Abu Huraira:Allah's Messenger (ﷺ) said, "When anyone of you stands for the prayers, Satan comes and puts him in doubts till he forgets how many rak`at he has prayed. So if this happens to anyone of you, he should perform two prostrations of Sahu while sitting
Reference: Bukhari 1232