Hadeeth Qudsi 35:

On the authority of AbuHurayrah (may Allah be pleased with him), who said that the Messengerof Allah   said:

Our Lord (glorified and exalted beHe) descends each night to the earth’s sky when there remains the finalthird of the night, and He says: Who is saying a prayer to Me that Imay 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 Hadeethends with the words:

And thus He continues till [thelight of] dawn shines.