617 - It was narrated from Salim ibn ‘Abdillah, from his father, that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Bilal gives the adhan at night, so [continue to eat and drink] until Ibn Umm Maktum gives the call to prayer.” Then he said: “He is a blind man; he does not give the call to prayer until he is told: Dawn has broken, dawn has broken.”.

Commentary : The practice of the Messenger of Allah (blessings and peace of Allah be upon him) was to have two adhans for Fajr prayer. The first was an adhan given at night, allowing enough time before the time for the prayer began so that one who was sleeping could wake up, and one who was praying qiyam could rest, and one who wanted to fast could eat sahur. The second was an adhan given when the time for Fajr began; this is the time when people stop eating and drinking, and begin the fast.
This hadith confirms that, as the Prophet (blessings and peace of Allah be upon him) explained, Bilal gave the adhan at the end of the night, before the break of dawn; therefore people did not have to stop eating and drinking, or begin the fast, until Ibn Umm Maktum gave the adhan. His real name was ‘Abdullah – or, it was said, ‘Amr ibn Za’idah. That was because he was the one who gave the call after the break of dawn. Ibn Umm Maktum was a blind man who did not give the call to Fajr prayer until he was certain that the dawn had broken; the people used to call out to him and tell him that the dawn had broken, so that Ibn Umm Maktum would know for certain that the time for Fajr had begun, and he would give the call to prayer.
This hadith indicates that it is permissible for the one who wants to fast to continue eating and drinking until the end of the time before Fajr.
It indicates that it is prescribed to have two mu’adhdhins in one mosque.
It indicates that it is permissible for the mu’adhdhin to be blind.
It indicates that it is permissible to refer to a person by mentioning his physical disabilities, so that people will know who is being referred to, if that person is well-known for having that disability, and it is not mentioned by way of shaming him or showing disrespect.
It indicates that it is permissible to name a man after his mother, if he is known by that name, as in the case of Ibn Umm Maktum..