The root of the disagreement is that the adhān vacillates between being regarded as one of the prayer’s own prescribed utterances and being viewed merely as a summons to assemble.
Section Three of the First Chapter: The Time of the Adhān
With respect to the time for giving the adhān, all scholars agree that it must not be called before the prayer’s appointed time—except in the case of the dawn prayer, over which they differed. Mālik and al-Shāfiʿī held that it is permissible to give its adhān before the break of dawn, whereas Abū Ḥanīfah prohibited this. Others maintained that if one calls for Fajr before dawn, a second adhān must follow after dawn, for in their view the obligatory call is the one given post-dawn.
Abū Muḥammad Ibn Ḥazm said that the dawn prayer must certainly have an adhān after its time; if one is made beforehand it is still valid, provided only a brief interval separates the two—no longer than the time it takes for the first caller to descend and the second to ascend.
Their divergence stems from two apparently contradictory ḥadīths. The first is the well-known, rigorously authenticated report in which the Prophet—peace and blessings be upon him—said: “Bilāl gives the call during the night, so eat and drink until Ibn Umm Maktūm gives the call.” Ibn Umm Maktūm was a blind man who would not call until it was said to him, “Morning has come, morning has come.”
The second report, transmitted from Ibn ʿUmar—may Allah be pleased with them both—states: “Bilāl once gave the adhān before the rise of dawn, so the Prophet—peace and blessings be upon him—ordered him to go back and announce, ‘Lo! the servant has fallen asleep.’”
The Ḥijāzī version is regarded as stronger, yet the Kūfan narration was also recorded by Abū Dāwūd and deemed sound by many scholars. Faced with these two reports, the scholars adopted one of two approaches: reconciliation or preference.
Those who opted for preference were the Ḥijāzīs, saying: “Bilāl’s ḥadīth is the more reliable and therefore binding.”
Those who strove for reconciliation were the Kūfans. They argued that Bilāl’s call may have occurred at a time of uncertainty about the dawn’s appearance—his eyesight being weak—whereas Ibn Umm Maktūm’s call came when daybreak was certain. Supporting this is the statement narrated from ʿĀʾishah: “The interval between their two adhāns was no more than the time it took for one of them to descend and the other to ascend.”
As for those who maintain that both calls should be combined—one before dawn and another after it—they do so in light of the specific practice reported for the dawn prayer: during the lifetime of the Messenger of Allah, peace and blessings be upon him, two muezzins were assigned to it, Bilāl and Ibn Umm Maktūm.