Musnad Ahmad 30:2890

'Abd al-Rahman narrated to us, he said: Shu'bah narrated to us, from Marwan al-Asfar and 'Ata' ibn Abi Maymunah, that they heard Abu Rafi' say: I saw Abu Hurayrah prostrate during [the recitation of] "When the sky has split [Idha al-sama'u inshaqqat]." I said: "Do you prostrate during it?" He said: "I saw my intimate friend, may Allah bless him and grant him peace, prostrate during it, so I will not cease to prostrate during it until I meet him."