Musnad Ahmad 30:2479

Yahya ibn Sa'id narrated to us, from Hisham, who said: Yahya narrated to us, from Abu Salamah, who said: I saw Abu Hurairah prostrate during "When the sky has split asunder" (Surah Al-Inshiqaq). I said, "Do you prostrate in it?" He said, "The Prophet, may Allah bless him and grant him peace, prostrated in it."