Sahih Bukhari Volume 9, Book 93, Hadith Number 586.

Narrated By Abu Huraira : Allah’s Apostle said, “Every night when it is the last third of the night, our Lord, the Superior, the Blessed, descends to the nearest heaven and says: Is there anyone to invoke Me that I may respond to his invocation? Is there anyone to ask Me so that I may grant him his request? Is there anyone asking My forgiveness so that I may forgive him?.” (See Hadith No. 246,Vol. 2)