Musnad Ahmad 30:2787

Muhammad ibn Ja‘far narrated to us, he said: Shu‘bah narrated to us, from ‘Ata’ ibn Abi Maymunah, from Abu Rafi‘, who said: I saw Abu Hurayrah prostrate during [the recitation of] "When the sky has split open" (Surah Al-Inshiqaq). I said: "Do you prostrate in it?" He said: "Yes, I saw my intimate friend (Khalil) prostrate in it, and I shall not cease to prostrate in it until I meet him." Shu‘bah said: I said: "The Prophet, peace and blessings of Allah be upon him?" He said: "Yes."