Sahih Muslim , Book 4, Hadith 748 (USC-MSA)

'Umar b. al-Khattab reported: The Messenger of Allah said: When the Mu'adhdhin says: Allah is the Greatest, Allah is the Greatest, and one of you should make this response: Allah is the Greatest, Allah is the Greatest; (and when the Mu'adhdhin) says: I testify that there is no god but Allah, one should respond: I testify that there is no god but Allah, and when he says: I testify that Muhammad is the Messenger of Allah, one should make a response: I testify that Muhammad is Allah's Messenger. When he (the Mu'adhdhin) says: Come to prayer, one should make a response: There is no might and no power except with Allah. When he (the Mu'adhdhin) says: Come to salvation, one should respond: There is no might and no power except with Allah, and when he (the Mu'adhdhin) says: Allah is the Greatest, Allah is the Greatest, then make a response: Allah is the Greatest, Allah is the Greatest. When he (the Mu'adhdhin) says: There is no god but Allah, and he who makes a re- sponse from the heart: There is no god but Allah, he will enter Paradise.

حَدَّثَنِي إِسْحَاقُ بْنُ مَنْصُورٍ، أَخْبَرَنَا أَبُو جَعْفَرٍ، مُحَمَّدُ بْنُ جَهْضَمٍ الثَّقَفِيُّ حَدَّثَنَا إِسْمَاعِيلُ بْنُ جَعْفَرٍ، عَنْ عُمَارَةَ بْنِ غَزِيَّةَ، عَنْ خُبَيْبِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ إِسَافٍ، عَنْ حَفْصِ بْنِ عَاصِمِ بْنِ عُمَرَ بْنِ الْخَطَّابِ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، عُمَرَ بْنِ الْخَطَّابِ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ إِذَا قَالَ الْمُؤَذِّنُ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ ‏.‏ فَقَالَ أَحَدُكُمُ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ ‏.‏ ثُمَّ قَالَ أَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ ‏.‏ قَالَ أَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ ثُمَّ قَالَ أَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ ‏.‏ قَالَ أَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ ‏.‏ ثُمَّ قَالَ حَىَّ عَلَى الصَّلاَةِ ‏.‏ قَالَ لاَ حَوْلَ وَلاَ قُوَّةَ إِلاَّ بِاللَّهِ ‏.‏ ثُمَّ قَالَ حَىَّ عَلَى الْفَلاَحِ ‏.‏ قَالَ لاَ حَوْلَ وَلاَ قُوَّةَ إِلاَّ بِاللَّهِ ‏.‏ ثُمَّ قَالَ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ ‏.‏ قَالَ اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ ‏.‏ ثُمَّ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ ‏.‏ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ ‏.‏ مِنْ قَلْبِهِ دَخَلَ الْجَنَّةَ ‏" ‏ ‏.‏

sunnah.com