Imam Bukhari narrates: Muhammad narrated to us, and he is Ibn Salam, he said: Abdul Wahhab informed us, he said: Khalid al-Hadhdha informed us from Abu Qilabah from Anas bin Malik, may Allāh be pleased with him, he said:
When the people became very numerous, they mentioned setting up some sign for the time of prayer, by which they would recognize the time. So they mentioned lighting a fire or striking a bell. Then Bilal, may Allāh be pleased with him, was commanded that he say the words of the Adhan twice each, and say the words of the Iqamah once each.
حَدَّثَنَا مُحَمَّدٌ هُوَ ابْنُ سَلاَمٍ، قَالَ أَخْبَرَنَا عَبْدُ الوَهَّابِ الثَّقَفِيُّ، قَالَ أَخْبَرَنَا خَالِدٌ الحَذَّاءُ، عَنْ أَبِي قِلاَبَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ
حَدَّثَنَا مُحَمَّدٌ هُوَ ابْنُ سَلاَمٍ، قَالَ أَخْبَرَنَا عَبْدُ الوَهَّابِ الثَّقَفِيُّ، قَالَ أَخْبَرَنَا خَالِدٌ الحَذَّاءُ، عَنْ أَبِي قِلاَبَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ لَمَّا كَثُرَ النَّاسُ قَالَ ذَكَرُوا أَنْ يَعْلَمُوا وَقْتَ الصَّلاَةِ بِشَيْءٍ يَعْرِفُونَهُ، فَذَكَرُوا أَنْ يُورُوا نَارًا، أَوْ يَضْرِبُوا نَاقُوسًا فَأُمِرَ بِلاَلٌ أَنْ يَشْفَعَ الأَذَانَ، وَأَنْ يُوتِرَ الإِقَامَةَ
Reference: Sahih Al Bukhari 606