Musnad Ahmad 30:2889

'Abd al-Rahman narrated to us, he said: Hisham narrated to us, from Yahya ibn Abi Kathir, from Abu Salamah, he said: I saw Abu Hurairah prostrate during [the recitation of] "When the sky has split [Idha al-sama'u inshaqqat]." I said: "Did I not see you prostrate in it?" He said: "If I had not seen the Prophet, may Allah bless him and grant him peace, prostrate in it, I would not have prostrated."