Musannaf Ibn Abi Shayba 35:351

Yazid narrated to us, from Ibn 'Awn, from Raja', from Qabisa ibn Dhu'ayb, who said: Abu Hurayra passed by me while I was praying, and he said, "Separate [them]." I did not understand what he said. When I finished, I said, "What [did you mean by] 'separate'?" He said, "Separate between the night prayer and the day prayer."