Musnad Abu Ya'la al-Mawsili 117:192

A funeral procession passed by the Messenger of Allah, may Allah bless him and grant him peace, and the people praised it with good. The Messenger of Allah, may Allah bless him and grant him peace, said, "It has become incumbent." Then another passed by, and they praised it with evil. The Messenger of Allah, may Allah bless him and grant him peace, 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, and the believers are the witnesses of Allah upon the earth."