Musnad Ahmad 30:2751

Muhammad ibn Ja‘far narrated to us, he said: Shu‘bah narrated to us, from Marwan al-Asfar, he said: I heard Abu Rafi‘ say: I saw Abu Hurayrah prostrate during [the recitation of] "When the sky has split asunder" (Surah Al-Inshiqaq). He said: So I asked him, and he said: "My beloved (Khalil), may Allah bless him and grant him peace, prostrated in it, and I will not cease to prostrate in it until I meet him."