Bulugh al-Maram

Lexical Explanation:
«أَذَّنَ قَبْلَ الْفَجْرِ» gave the call to prayer (adhan) before the break of dawn (fajr), based on the assumption that fajr had already begun (even though it had not). This refers to a time when giving the adhan before the true dawn (fajr sadiq) was not legislated.

Benefit:
In the beginning, only Sayyiduna Bilal radi Allahu anhu used to give the adhan. Later, when Sayyiduna Abdullah ibn Umm Maktum radi Allahu anhu was also appointed as a muezzin along with him, Sayyiduna Bilal radi Allahu anhu would give the first adhan before the true dawn (subh sadiq), and Sayyiduna Ibn Umm Maktum radi Allahu anhu would give the second adhan for the fajr prayer after the true dawn, as has been mentioned earlier.

Hadith Narrator:
(Sayyiduna Ibn Umm Maktum radi Allahu anhu) His name was Amr or Abdullah ibn Qays al-Qurashi al-Amiri, whose mention the commentators have made in the context of the revelation of Surah Abasa. He was among the early Muslims and had also migrated. The Prophet sallallahu alayhi wa sallam appointed him as his deputy (acting leader) in Madinah thirteen times during his absence, so that he would lead the people in prayer. He was blind. He attained martyrdom in the Battle of Qadisiyyah. On that day, the flag was in his hand.