Unfamiliar expressions:

1- “Bilal was commanded”: the verb is in the passive voice; the One who issued the command was the Prophet ﷺ, so the report is treated as marfūʿ (traced back to him). Scholars of legal methodology have differed over whether such passive constructions and the like necessarily entail a marfūʿ attribution. The sound position is that they do, for the obvious assumption is that the person authorized to issue a religious command is the Messenger ﷺ.

2- “to pronounce the adhan in pairs”: that is, every phrase of the adhan is said twice; a “pair” (shafʿ) means two occurrences.

3- “and to pronounce the iqamah singly”: meaning that each phrase of the iqamah is said once, for witr (odd) is the opposite of shafʿ (even).

Overall meaning:

The Prophet ﷺ instructed his mu’adhdhin, Bilal, to render the adhan in pairs because it serves to alert those who are still absent; accordingly, each phrase is repeated twice—apart from the opening takbir, which authentic reports show is said four times, and the concluding declaration of tawḥīd, which is uttered once.

He likewise ordered Bilal to pronounce the iqamah singly, for it is meant to notify those already present. Thus each of its phrases is said once—except for the opening takbir and the formula “qad qāmat al-ṣalāh” (“the prayer has been established”), both of which are authentically reported as being said twice.

Scholarly disagreement:

The jurists have differed regarding the legal status of the adhan and the iqamah.

Imam Ahmad, some Malikis, a number of Shafiʿis, and ʿAtaʾ maintain that they are communal obligations for adult men. They rely on many hadiths, including the one at hand, on the basis that a command implies obligation, as well as the two authentic narrations from Malik ibn al-Huwairith, “Let one of you give the adhan for you,” among others. They add that the two calls are conspicuous symbols of Islam, and those who abandon them may be fought.

Some of these scholars limit that obligation to men only, citing the sound report transmitted by al-Bayhaqi from Ibn ʿUmar: “Women are not required to give either adhan or iqamah.” Women are instructed to lower their voices and observe concealment, and congregation, which entails public assembly, is not incumbent upon them.

The Hanafis and most Shafiʿis hold that both calls are recommended sunnahs rather than obligatory. They cite what many leading Imams have authenticated: on the night at Muzdalifah the Prophet ﷺ did not give an adhan; he pronounced only the iqamah.