Musnad Ahmad 26:272

'Abd al-Samad narrated to us, 'Abd al-'Aziz ibn Muslim narrated to us, Abu Ishaq al-Hamdani narrated to us, from Abu al-Ahwas, from Ibn Mas'ud, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When the remaining third of the night is left, He descends to the lowest heaven, then He opens the gates of the heaven, then He spreads out His hand and says: 'Is there any petitioner who will be given his request?' And He continues like that until the dawn breaks."