Musnad Ahmad 26:420

Yahya ibn Adam and Yahya ibn Abi Bukayr narrated to us, they said: Isra'il narrated to us, from Abu Ishaq, from 'Abd al-Rahman ibn Yazid, from 'Abdullah ibn Mas'ud, who said: "The Messenger of Allah, peace and blessings of Allah be upon him, recited to me: 'Indeed, I am the Provider, the Possessor of Power, the Firm.'"