Musnad Ahmad 26:194

Yahya ibn Adam narrated to us, 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, may Allah bless him and grant him peace, recited to me: 'Indeed, it is I who am the Provider, the Possessor of Power, the Firm.'"