Musnad Abu Ya'la al-Mawsili 2:6

Shayban narrated to us, Dawud ibn Abi al-Furat narrated to us, Abdullah ibn Buraydah narrated to us, from Abu al-Aswad al-Du'ali, who said: I came to Medina, and a disease had occurred in it, and they were dying a rapid death. I sat with Umar ibn al-Khattab, and a funeral passed by him, and they praised its owner with good. Umar said, "It has become obligatory." Then another passed by, and they praised its owner 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 (peace and blessings of Allah be upon him) said: "Any Muslim for whom four bear witness to 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.