By this isnad from Ahmad b. Abi Abdillah. He said: Al-Husayn b. Yazid narrated to us from Isma`il b. Muslim from al-Sadiq Ja`far b. Muhammad from his father from his forefathers عليه السلام. He said: The Messenger of Allah صلى الله عليه وعلى آله وسلم said: Sitting in the mosque waiting for the prayer is worship for one who does not nullify. It was said: O Messenger of Allah! What is the nullifier? He said: Backbiting.