Abu Dawud Book 2, Hadith Number 1046.
Narated By Ali ibn AbuTalib : Ali said on the pulpit in the mosque of Kufah: When Friday comes, the devils go to the markets with their flags, and involve people in their needs and prevent them from the Friday prayer. The angels come early in the morning, sit at the door of the mosque, and record that so-and-so came at the first hour, and so-and-so came at the second hour until the imam comes out (for preaching).
When a man sits in a place where he can listen (to the sermon) and look (at the imam), where he remains silent and does not interrupt, he will receive a double reward. If he stays away, sits in a place where he cannot listen (to the sermon), silent, and does not interrupt, he will receive the reward only once. If he sits in a place where he can listen (to the sermon) and look (at the imam), and he does not remain silent, he will have the burden of it. If anyone says to his companion sitting besides him to be silent (while the imam is preaching), he is guilty of idle talk. Anyone who interrupts (during the sermon) will receive nothing (no reward) on that Friday.
Then he (the narrator) says in the end of this tradition: I heard the Apostle of Allah (PBUH) say so.