Musnad Ahmad 830:95

'Abd al-Razzaq narrated to us, Sufyan informed us, from Khalid al-Hadhdha', Ibn Abi Bakrah narrated to us, from Abu Bakrah, who said: We were with the Prophet, peace and blessings of Allah be upon him, when a man praised another man. The Prophet, peace and blessings of Allah be upon him, said: "You have broken his back. If one of you must praise his companion, let him say: 'I consider him so-and-so, and Allah is his reckoner, and I do not purify anyone before Allah; I consider him such-and-such,' if he knows that about him."