The Messenger of Allah (sallallahu alayhi wa sallam) said: “When you hear the Adhan repeat what the Muadhdhin (the call-maker) says.”.
وَعَنْ أَبِي سَعِيدٍ اَلْخُدْرِيِّ رضى الله عنه
قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -«إِذَا سَمِعْتُمْ اَلنِّدَاءَ، فَقُولُوا مِثْلَ مَا يَقُولُ اَلْمُؤَذِّنُ»
The Messenger of Allah (sallallahu alayhi wa sallam) said: “When you hear the Adhan repeat what the Muadhdhin (the call-maker) says.”.
صحيح. رواه البخاري (611)، ومسلم (383)
Who passed it on, from Ibn Hajar back to the one who was there.
The same words, in another collection.
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