It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that when the Muslims came to Madinah, they would gather and wait for the prayers, and there was no one to make the call. One day they spoke about this. Some said: Let us make a bell like the bell of the Christians, and some said: Rather a horn like that of the Jews. Sayyiduna Umar (may Allah be pleased with him) said: Why do you not send a man to call for the prayer? The Messenger of Allah (peace and blessings be upon him) said: "O Bilal, stand and call for the prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1924