Sahih Bukhari, Chapter: Funerals (Al-Janaaiz)

I came to Medina when an epidemic had broken out. While I was sitting with 'Umar bin Al-Khattab a funeral procession passed by and the people praised the deceased. 'Umar said, "It has been affirmed to him." And another funeral procession passed by and the people praised the deceased. 'Umar said, "It has been affirmed to him." A third (funeral procession) passed by and the people spoke badly of the deceased. He said, "It has been affirmed to him." I (Abu Al-Aswad) asked, "O chief of the believers! What has been affirmed?" He replied, "I said the same as the Prophet had said, that is: if four persons testify the piety of a Muslim, Allah will grant him Paradise." We asked, "If three persons testify his piety?" He (the Prophet) replied, "Even three." Then we asked, "If two?" He replied, "Even two." We did not ask him regarding one witness.