Musnad Abu Ya'la al-Mawsili 159:82

And with his chain of narration, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Angels succeed one another among you: angels of the night and angels of the day. Then they gather at the Asr prayer and the Fajr prayer. Then those who stayed among you ascend, and He asks them—while He is more knowing—saying: 'How did you leave My servants?' They say: 'We came to them while they were praying, and we left them while they were praying.'"