Musnad Abu Ya'la al-Mawsili 155:118

Abu Khaythama and al-Muqaddami narrated to us, they said: Sufyan ibn 'Uyaynah narrated to us, from al-Zuhri, from Abu Salamah, from Abu Hurayrah, attributing it to the Prophet, he said: "Satan comes to one of you while he is in his prayer and confuses him until he does not know how much he has prayed. So whoever finds anything of that, let him perform two prostrations while he is sitting."