Musnad Ahmad 1017:18

'Uthman ibn 'Umar narrated to us, Malik informed us, from Ibn Buraydah, from his father, who said: Buraydah went out at night, and the Prophet, peace and blessings of Allah be upon him, met him. He took his hand and brought him into the mosque, and there was the sound of a man reciting. The Prophet, peace and blessings of Allah be upon him, said: "Do you consider him a show-off?" Buraydah remained silent. Then there was a man supplicating, saying: "O Allah, I ask You by the fact that I bear witness that You are Allah, there is no god but You, the One, the Eternal Refuge, who neither begets nor is born, and to whom there is no equivalent." The Prophet, peace and blessings of Allah be upon him, said: "By the One in whose hand is my soul—or he said: By the One in whose hand is the soul of Muhammad—he has asked Allah by His Greatest Name, which, if He is asked by it, He gives, and if He is called upon by it, He answers." He said: When the next night came, Buraydah went out at night, and the Prophet, peace and blessings of Allah be upon him, met him. He took his hand and brought him into the mosque, and there was the sound of the man reciting. The Prophet, peace and blessings of Allah be upon him, said: "Do you call him a show-off?" Buraydah said: "Do you call him a show-off, O Messenger of Allah?" The Prophet, peace and blessings of Allah be upon him, said: "No, rather he is a believing, penitent man. No, rather he is a believing, penitent man." And there was Al-Ash'ari reciting with a voice he had in a corner of the mosque. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, Al-Ash'ari—or indeed, 'Abdullah ibn Qays—has been given a flute from the flutes of David." I said: "Shall I not inform him, O Messenger of Allah?" He said: "Yes, inform him." So I informed him, and he said: "You are a friend to me; you have informed me of a hadith from the Messenger of Allah, peace and blessings of Allah be upon him."