Mukhtasar Bukhari (Abridged) 370 — How adhan began

Narrated Ibn Umar (may Allah be pleased with them) that when the Muslims came to Madinah, they used to gather for prayer by estimating the time, and at that time, there was no formal call to prayer (adhan). One day, the Muslims discussed this matter (that there should be some announcement). Some suggested making a bell like the Christians’ bell, and some said no, rather make a horn like the Jews’ horn. Then Umar (may Allah be pleased with him) said, why not appoint a man who would call to prayer (give the adhan) for the prayer. So the Messenger of Allah (peace and blessings of Allah be upon him) said: “Bilal, get up and give the adhan for the prayer.”