On the authority of Abu Hurayrah (may Allah be pleased with him), who said that the Messenger of Allah (PBUH) said:

Our Lord (glorified and exalted be He) descends each night to the earth's sky when there remains the final third of the night, and He says: Who is saying a prayer to Me that I may answer it? Who is asking something of Me that I may give it him? Who is asking forgiveness of Me that I may forgive him?

It was related by al-Bukhari (also by Muslim, Malik, at-Tirmidhi and Abu Dawud).

In a version by Muslim the Hadith ends with the words:

And thus He continues till [the light of] dawn shines.