Musnad Ahmad 30:3413

Yazid narrated to us, Muhammad informed us, from Abu Salamah, from Abu Hurairah, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Allah, the Almighty and Majestic, descends every night to the lowest heaven during the latter half of the night—or the latter third of the night—and says: 'Who is it that calls upon Me, so that I may answer him? Who is it that asks of Me, so that I may give to him? Who is it that seeks My forgiveness, so that I may forgive him?' This continues until the dawn breaks, or until the reader finishes the morning prayer."