مُسْنَدُ أَحْمَدَ
Musnad Ahmad 1565
Musnad Abu Ishaq Sa'd bin Abi Waqqas
It was narrated from “Amir bin Sa"d bin Abi Waqqas, from his father Sa"d, that the Messenger of Allah (ﷺ) said: "Whoever says when he hears the mu"adhdhin; ‘And I bear witness that there is no God but Allah alone, with no partner or associate, and that Muhammad is His slave and His Messenger; I am content with Allah as my Lord, Muhammad as my Messenger and Islam as my religion, his sins will be forgiven him.
Musnad Ahmad 1565Sahih (Darussalam) [ Muslim (386)]