My father said that Allah s Apostle said, "Bilal pronounces 'Adhan at night, so keep on eating and drinking (Suhur) till Ibn Um Maktum pronounces Adhan." Salim added, "He was a blind man who would not pronounce the Adhan unless he was told that the day had dawned."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ بِلاَلاً يُؤَذِّنُ بِلَيْلٍ فَكُلُوا وَاشْرَبُوا حَتَّى يُنَادِيَ ابْنُ أُمِّ مَكْتُومٍ ثُمَّ قَالَ وَكَانَ رَجُلاً أَعْمَى لاَ يُنَادِي حَتَّى يُقَالَ لَهُ أَصْبَحْتَ أَصْبَحْتَ