After uttering Mu'adhdhin Tashahhud (i.e. Ashhadu Anna Muhammadar ...) the listeners will say this dhikr -
أَشْهَدُ أَنْ لَا إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لَا شَرِيكَ لَهُ وَأَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ رَضِيتُ بِاللَّهِ رَبًّا وَبِمُحَمَّدٍ رَسُولًا وَبِالْإِسْلَامِ دِينًا
Pronunciation
Ash-hadu an laa ilaaha ill-Allahu wa'hdahu laa shareeka lahu wa anna mu'hammadan ‛abduhu wa rasooluhu, radeetu billaahi rabban wa bimu'hammadin rasoolan wa bil -islaami deen-an
Meaning
I bear witness that none has the right to be worshipped except Allah, alone, without partner, and that Muhammad is His slave and Messenger (ﷺ). I am pleased with Allah as a Lord, and Muhammad as a Messenger and Islam as a religion. Sa'd ibn Abi Waqqas (RA) said: The Messenger of Allah (ﷺ) said: "Whoever hears Mu'adhzin and utters these words, all his sins will be forgiven."
Source: Muslim: 386
Read the hadith
حَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ، أَخْبَرَنَا اللَّيْثُ، عَنِ الْحُكَيْمِ بْنِ عَبْدِ اللَّهِ بْنِ قَيْسٍ الْقُرَشِيِّ، ح وَحَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا لَيْثٌ، عَنِ الْحُكَيْمِ بْنِ عَبْدِ اللَّهِ، عَنْ عَامِرِ بْنِ سَعْدِ بْنِ أَبِي وَقَّاصٍ، عَنْ سَعْدِ بْنِ أَبِي وَقَّاصٍ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم أَنَّهُ قَالَ " مَنْ قَالَ حِينَ يَسْمَعُ الْمُؤَذِّنَ أَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ وَأَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ رَضِيتُ بِاللَّهِ رَبًّا وَبِمُحَمَّدٍ رَسُولاً وَبِالإِسْلاَمِ دِينًا . غُفِرَ لَهُ ذَنْبُهُ " . قَالَ ابْنُ رُمْحٍ فِي رِوَايَتِهِ " مَنْ قَالَ حِينَ يَسْمَعُ الْمُؤَذِّنَ وَأَنَا أَشْهَدُ " . وَلَمْ يَذْكُرْ قُتَيْبَةُ قَوْلَهُ وَأَنَا .
Sa'd b. Abu Waqqas reported: The Messenger of Allah (ﷺ) said: If anyone says on hearing the Mu'adhdhin: I testify that there is no god but Allah alone. Who has no partner, and that Muhammad is His servant and His Messenger, (and that) I am satisfied with Allah as my Lord, with Muhammad as Messenger. and with Islam as din (code of life), his sins would be forgiven. In the narration transmitted by Ibn Rumh the words are:" He who said on hearing the Mu'adhdhin and verity I testify." ' Qutaiba has not mentioned his words:" And I." [Muslim: 386]
Duas from IslamicAPI's Masnun Dua dataset (based on the Quran, hadith, Hisnul Muslim and Rahe Belayat). See the dataset