Musannaf Ibn Abi Shayba 27:68

Abdullah bin Numayr narrated to us, he said: Musa bin Muslim narrated to us, from Abd al-Rahman bin Sabit, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah manifested Himself to me in the most beautiful form, and He asked me: 'Regarding what do the Highest Assembly dispute?' I said: 'My Lord, I have no knowledge of it.' He said: 'So He placed His hand between my shoulders, and there was nothing He asked me about except that I knew it.'"