Musnad Ahmad 31:891

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Abu Ishaq, from al-Agharr Abu Muslim, from Abu Hurayrah and Abu Sa'id al-Khudri, from the Messenger of Allah, peace and blessings of Allah be upon him, who said: "No people gather remembering Allah, except that the angels surround them, mercy covers them, tranquility descends upon them, and Allah mentions them to those who are with Him." And he said: "Indeed, Allah grants respite until, when the last third of the night remains, Allah, the Mighty and Majestic, descends to this heaven and calls out: 'Is there any sinner who will repent? Is there any seeker of forgiveness? Is there any supplicant? Is there any asker?' until the dawn."