Wahi – Divine Inspirations and Revelations
How was Adhaan received
The Adhaan (call to prayer) was seen in a dream by two of Prophet’s companions, Abdullah b. Zayd b. Thalaba (r.a) and Umar ibn Al Khattab (r.a). They both saw the vision during the life of Prophet Muhammad ﷺ and not after him. After seeing this vision they both informed the Prophet ﷺ who himself confirmed that this dream was from Allah ﷻ and thus the adhaan that echoes fives time a day throughout the Muslim world, for past fifteen centuries, is that same one (with slight difference in wording in some Muslim regions). Therefore one thing should be clear that adhaan came to be received at a time when guidance continued to descend to the Prophet and process of revelation was not complete yet. Now the question comes how companions could receive knowledge from unseen when primary recipient of such knowledge was the Prophet ﷺ? Allah ﷻ would reveal knowledge of al-ghayb (unseen) to the Prophet ﷺ through various channels including dreams and at times the recipient would be a companion rather than the Prophet himself. Please refer to the previous post on Dreams - Part of Prophethood to learn more. Based on what Islam has explained about this part of prophethood we can understand why the knowledge of adhaan was revealed to one of the Prophet’s companions:
“When the Messenger first came, the people gathered to him for prayer at the appointed times without being summoned. At first the messenger thought of using a trumpet like that of the Jews who used it to summon to prayer. Afterwards he disliked the idea and ordered a clapper to be made, so it was duly fashioned to be beaten when the Muslims should pray. Meanwhile Abdullah b. Zayd b. Thalaba, brother of al-Harith, heard a voice in a dream, and came to the messenger saying: ‘A phantom visited me in the night. There passed by me a man wearing two green garments carrying a clapper in his hand, and I asked him to sell it to me. When he asked me what I wanted it for I told him that it was to summon people to prayer, whereupon he offered to show me a better way: it was to say thrice: “Allahu Akbar. I bear witness that there is no God but Allah I bear witness that Muhammad is the Messenger of Allah. Come to prayer. Come to prayer. Come to divine service. Come to divine service. Allahu Akbar. Allahu Akbar. There is no God but Allah”. When the Messenger was told of this he said that it was a true vision if God so willed it, and that he should go with Bilal and communicate it to him so that he might call to prayer thus, for he had a more penetrating voice. When Bilal acted as muezzin Umar heard him in the house and came to the Messenger dragging his cloak on the ground and saying that he had seen precisely the same vision. The Messenger said: “Allah be praised for that!”’
Therefore in Islamic traditions and its teachings Muslims are supposed to have faith that good and true dreams called bushra or al-mubashiraat are seen by the believers not only for themselves but for other believers as well. They are part of prophet hood even after the revelation process is complete with the arrival of Quran. But moving forward, their news does not include any revelation on religious matters because Islam is completed with the arrival of the Quran. Allah ﷻ will leave this one part available till the end of the world to communicate news of al-ghayb (unseen) to believers regarding their personal lives, if and when He seems correct.
 Dreams in Islam - A window to the truth and to the heart by Imran N. Hosein - Published by Masjid Darul Qur’an – New Edition 2001