The Excellence of the Adhan and the Response to the Mu’adhdhin - Section 1 Mishkat al-Masabih 661
Arabic hadith text
وَعَنْ سَعْدِ بْنِ أَبِي وَقَّاصٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنَّهُ قَالَ: «مَنْ قَالَ حِينَ يَسْمَعُ الْمُؤَذِّنَ أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيكَ لَهُ وَأَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ رَضِيتُ بِاللَّهِ رَبًّا وَبِمُحَمَّدٍ رَسُولًا وَبِالْإِسْلَامِ دِينًا غُفِرَ لَهُ ذَنبه» . رَوَاهُ مُسلم
Translation
Sa‘d b. Abu Waqqas reported God’s Messenger as saying
If anyone says when he hears the mu’adhdhin, “I testify that there is no god but God alone who has no partner and that Muhammad is His servant and Messenger; I am satisfied with God as Lord, with Muhammad as Messenger, and with Islam as religion,” his sins will be forgiven him. Muslim transmitted it.