Nafi' narrated that 'Abdullah bin 'Umar used to say:
When the Muslims arrived in Al-Madinah they used to gather and try to figure out the time for prayer, and no one gave the call to prayer. One day they spoke about that; some of them said: 'Let us use a bell like the Christians do;' others said, 'No, a horn like the Jews have.' 'Umar, may ,Allah be pleased with him, said: 'Why don't you send a man to announce the time of prayer?' The Messenger of Allah (ﷺ) said: 'O Bilal, get up and give the call to prayer.'