It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you stands to pray, Satan comes to him and puts him into confusion (about the prayer), until he does not know how much he has prayed. So when any of you experiences that, let him perform two prostrations while sitting."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3798