Musnad Abu Ya'la al-Mawsili 117:78

Abu al-Rabi' narrated to us, Hammad narrated to us, Thabit narrated from Anas bin Malik, who said: A funeral procession passed by the Prophet, may Allah bless him and grant him peace, and they praised it with good. He said, "It has become incumbent." Then another funeral procession passed by him, and they praised it with evil. He said, "It has become incumbent." It was said, "O Messenger of Allah, you said for this one 'it has become incumbent' and for this one 'it has become incumbent'?" He said, "The testimony of the people."