مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4240
Musnad of Abdullah bin Mas'ood
It was narrated from ‘Abdullah that The Prophet (ﷺ) said: "Verily Allah, may He be glorified and exalted, opens the gates of heaven in the last third of the night, then He descends to the lowest heaven, then He stretches out His hand, then He says: 'Is there any slave who will ask Me so that I may give him?" until dawn breaks."
Musnad Ahmad 4268A saheeh hadeeth]