Musnad Ahmad 2:123

'Abdullah ibn Yazid narrated to us, Dawud—meaning Ibn Abi al-Furat—narrated to us, 'Abdullah ibn Buraydah narrated to me, from Abu al-Aswad al-Du'ali, who said: I came to Medina, and a disease had broken out in it, and they were dying a rapid death. I sat with 'Umar ibn al-Khattab, and a funeral passed by him, and the deceased was praised with good. 'Umar said: "It has become incumbent." Then another passed by, and the deceased was praised with good, and he said: "It has become incumbent." Then a third passed by, and the deceased was praised with evil, and 'Umar said: "It has become incumbent." I said: "What has become incumbent, 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.'" He said: "We said: 'Or three?' He said: 'Or three.' We said: 'Or two?' He said: 'Or two.' Then we did not ask him about one."