The Messenger of Allah ﷺ said, "Bilal calls the adhan at night, so eat and drink until Ibn Umm Maktum makes his call." Then the narrator added, "He was a blind man who would not call until it was said to him, 'Morning has come, morning has come.'"
أن رسول الله ﷺ قال: إن بلالا يؤذن بليل، فكلوا واشربوا حتى ينادي ابن أم مكتوم ثم قال: وكان رجلا أعمى، لا ينادي حتى يقال له: أصبحت أصبحت.
Malik narrated it in the Book of Prayer (14), from Abdullah bin Dinar, from Ibn Umar, and he related the hadith. Bukhari narrated it in the Book of Adhan (617, 620) through the route of Malik, with the same wording, similarly. He also narrated it in the Book of Fasting (1918), from Ubayd bin Ismail, from Abu Usama, from Ubaydullah, from Nafi, from Ibn Umar. Then he followed it with the hadith of Ayesha that comes next.Muslim narrated it in the Book of Fasting (1092) through other routes besides the route of Ibn Dinar, from Ibn Umar, with similar wording. In one of his versions, through the route of Nafi, from Ibn Umar, he said, "The Messenger of Allah ﷺ had two muezzins, Bilal and Ibn Umm Maktum, the blind man. The Messenger of Allah ﷺ said, 'Bilal calls the adhan while it is still night, so eat and drink until Ibn Umm Maktum calls the adhan.'" He said, "There was no interval between them except that this one would come down and that one would go up."His statement, "There was no interval between them... etc," means that Bilal used to call the adhan before Fajr and would wait after his adhan for supplication and the like, then he would watch for Fajr. When its rising drew near, he would come down and inform Ibn Umm Maktum, who would then prepare himself with purification and other matters, and then go up and begin the adhan with the very first appearance of Fajr.