When the Muslims came to Medina, they gathered and sought to know the time of prayer but no one summoned them. One day they discussed the matter, and some of them said: Use something like the bell of the Christians and some of them said: Use horn like that of the Jews. Umar said: Why may not a be appointed who should call (people) to prayer? The Messenger of Allah ﷺ said: O Bilal, get up and summon (the people) to prayer. (Using translation from Muslim 377)  

أَنَّهُ كَانَ يَقُولُ كَانَ الْمُسْلِمُونَ حِينَ قَدِمُوا الْمَدِينَةَ يَجْتَمِعُونَ فَيَتَحَيَّنُونَ الصَّلَاةَ وَلَيْسَ يُنَادِي لَهَا أَحَدٌ فَتَكَلَّمُوا يَوْمًا فِي ذَلِكَ فَقَالَ بَعْضُهُمْ اتَّخِذُوا نَاقُوسًا مِثْلَ نَاقُوسِ النَّصَارَى وَقَالَ بَعْضُهُمْ بَلْ قَرْنًا مِثْلَ قَرْنِ الْيَهُودِ فَقَالَ عُمَرُ أَوْلَا تَبْعَثُونَ رَجُلًا يُنَادِي بِالصَّلَاةِ فَقَالَ رَسُولُ اللهِ ﷺ «يَا بِلَالُ قُمْ فَنَادِ بِالصَّلَاةِ»