question #3 Sahih al-Bukhari 3457, Book 60, Hadith 124 : What instructions were given to Bilal regarding the Adhan and Iqama?

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.”