Sayyiduna Salamah bin al-Akwa' (may Allah be pleased with him) narrates: We were with the Prophet (peace and blessings be upon him) when a funeral was brought, and the people said: You were such, and you were such. Then another funeral was brought, and the people said: You were such, and you were such. Thus they praised one with good and spoke ill of the other. The Messenger of Allah (peace and blessings be upon him) said: "You are Allah's witnesses on the earth, and the angels are Allah's witnesses in the heaven."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6232