Sahih al-Bukhari Book 10, Hadith 15
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."
Once on a rainy muddy day, Ibn `Abbas delivered a sermon in our presence and when the Mu'adhdhin pronounced the Adhan and said, "Haiyi `ala-s-sala(t) (come for the prayer)" Ibn `Abbas ordered him to say 'Pray at your homes.' The people began to look at each other (surprisingly). Ibn `Abbas said. "It was done by one who was much better than I (i.e. the Prophet (ﷺ) or his Mu'adh-dhin), and it is a license.'
When the Mu'adh-dhin pronounced the Adhan for Fajr prayer and the dawn became evident the Prophet ordered a two rak`at light prayer (Sunna) before the Iqama of the compulsory (congregational) prayer.