Musnad Ahmad 30:2029

Mu'awiyah ibn 'Amr narrated to us, he said: Za'idah narrated to us, from al-A'mash, from Abu Salih, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "The angels of the night and the angels of the day gather at the dawn prayer and the afternoon prayer." He said: "They gather at the dawn prayer." He said: "Then the angels of the night ascend, and the angels of the day remain." He said: "And they gather at the afternoon prayer." He said: "Then the angels of the day ascend, and the angels of the night remain." He said: "Then their Lord asks them: 'How did you leave My servants?'" He said: "They say: 'We came to them while they were praying, and we left them while they were praying.'" Sulayman said: "And I do not know it except that he said in it: 'So forgive them on the Day of Judgment.'"