Sahih al-Bukhari 3457
Sahih al-Bukhari · Book 60: Prophets · What has been said about Bani Israel
Narrated Anas:
حَدَّثَنَا عِمْرَانُ بْنُ مَيْسَرَةَ ، حَدَّثَنَا عَبْدُ الْوَارِثِ ، حَدَّثَنَا خَالِدٌ ، عَنْ أَبِي قِلاَبَةَ ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ ذَكَرُوا النَّارَ وَالنَّاقُوسَ، فَذَكَرُوا الْيَهُودَ وَالنَّصَارَى، فَأُمِرَ بِلاَلٌ أَنْ يَشْفَعَ الأَذَانَ وَأَنْ يُوتِرَ الإِقَامَةَ.
The people mentioned the fire and the bell (as means proposed for announcing the time of prayer) and by such a suggestion they referred to the Jews and the Christians. But Bilal was ordered, "Pronounce the words of the Adhan (i.e. call for the prayer) twice and the Iqama once only."