Musnad Ahmad 32:996

Yunus ibn Muhammad narrated to us, Hammad—meaning ibn Zayd—narrated to us, from Thabit, from Anas, who said: A funeral procession passed by the Messenger of Allah, may Allah bless him and grant him peace, and the people praised it with good. He said: "It has become incumbent." Then another funeral procession passed by, and it was praised with evil. He said: "It has become incumbent." They said: "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."