Imam Bukhari narrates: Mahmud bin Ghailan narrated to us, he said: Abdul Razzaq narrated to us, he said: Ibn Juraij informed us, he said: Nafi' informed me that Ibn Umar, may Allāh be pleased with them both, used to relate that

when the Muslims came to Madinah, they used to gather at the time of prayer, and no announcement was made for the prayer. So one day they consulted about this matter. Some of them said: Make something like a bell of the Christians. And some said: Make something like a horn of the Jews. Then Umar said: Why do you not send a man to announce the prayer? Then the Messenger of Allāh ﷺ said: O Bilal! Stand up and announce the prayer!