Sahih (Sahih al-Bukhari)
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.
Narrated Anas: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