Musannaf Ibn Abi Shayba 3:4255

Yazid ibn Harun 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 [the prayers]." I did not understand what he said. When I finished, I said, "What is 'separate'?" He said, "Between the night prayer and the day prayer."