Sahih al-Bukhari 611
Book 10: Call to Prayers (Adhaan) · Narrated by Abu Sa`id Al-Khudri
Arabic
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنِ ابْنِ شِهَابٍ، عَنْ عَطَاءِ بْنِ يَزِيدَ اللَّيْثِيِّ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " إِذَا سَمِعْتُمُ النِّدَاءَ فَقُولُوا مِثْلَ ما يَقُولُ الْمُؤَذِّنُ ".
English translation
Narrated Abu Sa`id Al-Khudri:Allah's Messenger (ﷺ) said, "Whenever you hear the Adhan, say what the Mu'adh-dhin is saying
Reference: Sahih al-Bukhari 611, Book of Call to Prayers (Adhaan). English translation by Dr. Muhammad Muhsin Khan.