From Sahih Muslim (Hadith 1776):
Abu Sa'id and Abu Huraira reported Allah's Messenger (ﷺ) as saying:Allah waits till when one-third of the first part of the night is over; He descends to the lowest heaven and says: It there any supplicator of forgiveness? Is there any penitant? Is there any petitioner (for mercy and favour)? Is there any solicitor? -till it is daybreak
Reference: Muslim 1776