The Messenger of Allah ﷺ said, "Whoever says when he hears the caller to prayer, 'I bear witness that there is no god but Allah alone, with no partner, and that Muhammad is His servant and messenger. I am content with Allah as my Lord, with Muhammad as my Messenger, and with Islam as my religion,' his sins will be forgiven."
عن رسول الله ﷺ أنه قال: من قال حين يسمع المؤذن: أشهد أن لا إله إلا الله وحده لا شريك له، وأن محمدا عبده ورسوله، رضيت بالله ربا، وبمحمد رسولا، وبالإسلام دينا غفر له ذنبه.