It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that a funeral passed by the Noble Prophet (peace and blessings be upon him). People began to mention the good qualities and praise of the deceased. The Noble Prophet (peace and blessings be upon him) said, "It has become obligatory." In the meantime, another funeral passed by and people mentioned the bad qualities and condemnation of the deceased. The Noble Prophet (peace and blessings be upon him) said, "It has become obligatory." Then he said, "You people are Allah's witnesses on earth."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 7552
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد حسن.