Sayyiduna Anas (may Allah be pleased with him) said: A funeral was passed by the Prophet (peace and blessings be upon him), and it was praised with good, so the Prophet (peace and blessings be upon him) said: "It has become obligatory." Another funeral was passed by, and it was spoken of badly; he (peace and blessings be upon him) said: "It has become obligatory." Then he (peace and blessings be upon him) was asked: Did you (peace and blessings be upon him) say of both that it has become obligatory? He (peace and blessings be upon him) said: "The believers are Allah's witnesses on the earth."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20910