Sunan at-Tirmithiy كتاب الصلاة باب ما جاء ما يقول الرجل إذا أذن المؤذن من الدعاء

حَدَّثَنَا قُتَيْبَةُ حَدَّثَنَا اللَّيْثُ عَنِ الْحُكَيْمِ بْنِ عَبْدِ اللَّهِ بْنِ قَيْسٍ عَنْ عَامِرِ بْنِ سَعْدٍ عَنْ سَعْدِ بْنِ أَبِى وَقَّاصٍ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ مَنْ قَالَ حِينَ يَسْمَعُ الْمُؤَذِّنَ وَأَنَا 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 أَبُو عِيسَى وَهَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ غَرِيبٌ لاَ نَعْرِفُهُ إِلاَّ مِنْ حَدِيثِ اللَّيْثِ بْنِ سَعْدٍ عَنْ حُكَيْمِ بْنِ عَبْدِ اللَّهِ بْنِ قَيْسٍ.
The Messenger of God, peace and blessings of God be upon him, said, "Whoever says upon hearing the caller to prayer, 'and I bear witness that there is no god except Allāh1 alone, who has no partners; and that Muhammad is His bondsman and messenger. I am satisfied with Allah as Lord, Muhammad as messenger, and Islam as religion,' will have his sins forgiven." Footnote: (1) Allāh is the Arabic name for the One and Only God, the same God shared by all monotheistic faiths (the name Allāh is often used by Arabic-speaking Christians and Jews). The name Allāh encompasses all the divine names and attributes of the Lord of the worlds, and hence has vast scopes of meaning. It is for this reason that Muslims consider it unique. Unlike the word 'God', Allāh in Arabic has no inflections of gender or number. Click on ḥadīth to read more