It is narrated from Imam Nafi that Sayyiduna Abdullah bin Umar (may Allah be pleased with him) said: When the Muslims migrated to Madinah Munawwarah, they used to gather and wait for the time of prayer, and at that time there was no one to give the adhan. One day the companions began to discuss this matter. Some said, "Make a bell like the Christians' bell." Some said, "There should not be a bell, but rather appoint a horn like the Jews have." Sayyiduna Umar (may Allah be pleased with him) said, "Why don't you do it this way: send someone to announce the prayer?" So the Messenger of Allah (peace and blessings be upon him) said, "Bilal! Get up and announce the prayer."