Musnad Ahmad 30:2675

Yazid narrated to us, he said: Muhammad ibn ‘Amr informed us, from Abu Salamah, who said: I saw Abu Hurairah prostrate during [the recitation of] "When the sky has split open" (Surah Al-Inshiqaq). I said: "You prostrated in a Surah that we do not prostrate in?" He said: "I saw the Messenger of Allah, peace and blessings of Allah be upon him, prostrate in it."