Musannaf Ibn Abi Shayba 6:1197

'Affan narrated to us, Dawud ibn Abi al-Furat narrated to us, from 'Abdullah ibn Buraydah, from Abu al-Aswad al-Du'ali, who said: I arrived in Medina while a disease had broken out in it, and I sat with 'Umar ibn al-Khattab. A funeral procession passed by them, and they praised its owner with good. 'Umar said, "It has become obligatory." Then another passed by, and they praised it with evil. 'Umar said, "It has become obligatory." Abu al-Aswad said: I said, "What has become obligatory, O Commander of the Faithful?" He said: I said as the Messenger of Allah (may Allah bless him and grant him peace) said: "Any Muslim for whom four bear witness with good, Allah will cause him to enter Paradise." We said: "And three?" He said: "And three." We said: "And two?" He said: "And two." Then we did not ask him about one.