Musnad Ahmad 1034:114

'Affan narrated to us, Hammam narrated to us, al-Hajjaj ibn Farafisa narrated to us, a man narrated to me, from Hudhayfah ibn al-Yaman, that he came to the Prophet, peace and blessings of Allah be upon him, and said: "While I was praying, I heard a speaker saying: 'O Allah, to You belongs all praise, and to You belongs all dominion, in Your hand is all good, and to You returns all matters, the public and the private thereof. You are worthy of being praised, for You are over all things competent. O Allah, forgive me all my past sins, protect me in what remains of my life, and grant me righteous deeds that You are pleased with me for.'" The Prophet, peace and blessings of Allah be upon him, said: "That was an angel who came to you to teach you how to praise your Lord."