Musnad Ahmad 26:224

Abu Sa'id narrated to us, Isra'il narrated to us, Abu Ishaq narrated to us, from 'Abd al-Rahman ibn Yazid, from 'Abdullah, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) taught me to recite: 'Indeed, it is Allah who is the Provider, the Possessor of Power, the Firm.'"