Sahih Bukhari Volume 002, Book 019, Hadith Number 180.

Narated By Abu Salma : I saw Abu Huraira reciting Idha-Sama' un-Shaqqat and he prostrated during its recitation. I asked Abu Huraira, "Didn't I see you prostrating?" Abu Huraira said, "Had I not seen the Prophet prostrating, I would not have prostrated."