Sahih Muslim | Book 42 | Hadith Number 7139

Narrated by 'Abd al-Rahman b. Abu Bakra
'Abd al-Rahman b. Abu Bakra reported on the authority of his father that a person praised another person in the presence of Allah's Apostle (may peace be upon him), whereupon he said: Woe be to thee, you have broken the neck of your friend, you have broken the neck of your friend-he said this twice. If one of you has to praise his friend at all, he should say: I think (him to be) so and Allah knows it well and I do not know the secret of the heart and Allah knows the destined end, and I cannot testify his purity against Allah but (he appears) to be so and so.