Sa’d b. Abi Waqqas reported the Messenger of Allah ﷺ as saying :
If anyone says when he hears the MU’ADHDHIN : “And I testify that there is no god but Allah alone who has no partner and that Muhammad is His servant and Apostle: I am satisfied with Allah as lord, with Muhammad as apostle and with Islam as religion”, he will be forgiven.

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا اللَّيْثُ، عَنِ الْحُكَيْمِ بْنِ عَبْدِ اللَّهِ بْنِ قَيْسٍ، عَنْ عَامِرِ بْنِ سَعْدِ بْنِ أَبِي وَقَّاصٍ، عَنْ سَعْدِ بْنِ أَبِي وَقَّاصٍ، عَنْ رَسُولِ اللَّهِ ﷺ قَالَ " مَنْ قَالَ حِينَ يَسْمَعُ الْمُؤَذِّنَ وَأَنَا أَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ وَأَشْهَدُ أَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ رَضِيتُ بِاللَّهِ رَبًّا وَبِمُحَمَّدٍ رَسُولاً وَبِالإِسْلاَمِ دِينًا غُفِرَ لَهُ " .