Musannaf Ibn Abi Shayba 3:4238

Hushaym narrated to us, from Abu Hurrah, from al-Hasan, that a man asked Abu Dharr: "Which part of the night is most heard [i.e., most likely to be answered]?" He said: "The middle of the night." He said: "And who is capable of that?" He said: "Whoever fears, sets out early."