"..You people are Allaah's witnesses on earth.."

1) Narrated Anas bin Malik, :

A funeral procession passed and the people praised the deceased. The Prophet said, "It has been affirmed to him." Then another funeral procession passed and the people spoke badly of the deceased. The Prophet said, "It has been affirmed to him". 'Umar bin Al-Khattab asked (Allah's Apostle (p.b.u.h) ), "What has been affirmed?" He replied, "You praised this, so Paradise has been affirmed to him; and you spoke badly of this, so Hell has been affirmed to him. You people are Allah's witnesses on earth."

Sahih al-Bukhari

2) Narrated Abu Al-Aswad:

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.

Sahih al-Bukhari