Musnad Ahmad 830:89

'Affan narrated to us, Wuhayb and Yazid—meaning Ibn Zuray'—narrated to us, they both said: Khalid al-Hadhdha' narrated to us, from 'Abd al-Rahman ibn Abi Bakrah, from Abu Bakrah, who said: A man praised another man in the presence of the Prophet, peace and blessings of Allah be upon him. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Woe to you! You have cut the neck of your companion," repeating it several times. "If one of you must praise his companion, then let him say: 'I consider such-and-such to be so-and-so, and Allah is his reckoner, and I do not purify anyone before Allah,' if he knows that to be the case, 'I consider him to be such-and-such.'"