Bilal would often hear about Muhammad (saw), and Islam, through the alarming discussions between his master and guests. Soon he felt drawn to this religion. He would listen to Abu Bakr calling to Islam, and slowly his heart was filled with Imaan. He went with Abu Bakr to the Prophet (saw) and declared his submission to Islam. This was a daring move from a slave who belonged to a staunch enemy of Muhammad. He was the seventh person to accept Islam. Abu Bakr and others of the same tribal status, were spared from harm by the Quraysh. However, the wrath of the disbelievers fell upon the Muslims who had no tribe to defend them. 'Umayyah ibn Khalaf used to force Bilal to go outside during the hottest part of the day wearing a suit of armour where he would then be thrown face down in the sand and leave him to bake in the sun. He would not return except to turn him on his back. He would have a gigantic rock placed on his chest and then say, "You will stay here until you die or deny Muhammad and worship al-Lat and al-'Uzzah."
Bilal used to endure this only by saying, "One, One." Abu Bakr passed by one day while they were torturing him. He said to 'Umayyah, "Have you no fear of Allah that you treat this poor man like this?" 'Umayyah replied, "You are the one who corrupted him, so you save him from his plight!" Abu Bakr replied, "Then sell him to me, you can state your price." 'Umayyah who was not to let a good deal pass by, he then sell Bilal and said, "I would have sold him to you even if you had offered me but an ounce of gold." Abu Bakr answered, "I would have bought him even if you asked a hundred ounces." Abu Bakr and Bilal went to the Prophet (saw) with the good news. There he announced, "I am setting Bilal free, O Messenger of Allah." This greatly pleased the Prophet (saw) not to mention Bilal himself.
When the Muslims were settled in Madinah, Islam became firmly established - salah, zak'at and fasting were instituted. In the beginning, Muslims gathered for salah at the appointed times without being summoned. Later the Prophet (saw) thought about using a trumpet like that the Jews used to summon to salah. He disliked the idea and ordered a clapper to be made to be beaten at salah times.
Then 'Abdullah ibn Zayd came to him and said, "O Messenger of Allah, I had a dream last night. A man wearing two green garments came to me holding a bell, so I offered to buy it. When he asked me what I wanted it for, I told him that it was to summon people to salah, whereupon he offered to show me a better way. It was to say four times, 'Allahu Akbar', then to say twice, 'ash-shadu alla ilaha illa Allah', then twice, 'ash-hadu anna Muhammad ur-rasulullah', then twice, 'hayyah 'alas-salah', then twice, 'hayyah 'alal-falah', then 'Allahu Akbar, Allahu Akbar, laa ilaha illa Allah.' "
"It is a true vision insha'Allah," said the Prophet (saw) adding, "Go and teach it to Bilal for he has a more beautiful and far reaching voice." For the first time Madinah resonated with the adhan as Bilal was saying it. It was only fitting that the one who uttered the word of Tawhid under the harshest of torture should utter it during the adhan. When 'Umar heard the adhan he rushed to the Prophet and said, "By the One Who has sent you with the Truth I had the same dream about it!". Revelation has already preceded you," replied the Prophet (saw).
Badr was a day etched in Bilal's memory. Quraysh was inflicted a heavy defeat and many were taken prisoner. Among them was 'Umayyah. When Bilal saw him, the memories of what he, and other Muslims, has endured in Makkah came rushing back to him. He exclaimed, "The arch-enemy of Allah - 'Umayyah ibn Khalaf! May I not live if he lives!" Now 'Umayyah was 'Abdur-Rahman ibn Awf's prisoner, and this fact dissuaded Bilal from attacking 'Umayyah himself. But, because Bilal kept crying these words, one of the Sahabah killed Umayyah with his sword.
The Prophet (saw) entered the conquest of Makkah not as a proud conquerer, but as a humble servant of Allah. He bowed his so low that it almost touched his mount. After he ordered that all idols be destroyed, he stood at the door of the Kaa'bah and said, "There is no god but Allah alone. He has no associate ... O Quraysh, Allah has taken you from the haughtiness of jahiliyyah and its veneration of ancestors. Man springs from Adam and Adam sprang from dust," then he recited verses from the Qur'an until he said, "Verily the most noble of you in Allah's sight is the most pious." [Al-Qur'an 49:13] He ordered Bilal to make the adhan on the rooftop of the Kaab'ah. Hearing his voice, a disbeliever exclaimed, "Look at this black man!" His friend replied, "When Allah hates someone he turns him to the worst." History however attests that Bilal occupied a distinguished position among the Prophet's Companions. 'Umar would often say, "Abu Bakr is our master and he freed our master." Meaning Bilal. But Bilal would say, "I am only a man who used to be a slave."
Bilal was mu'adhin (the caller to salah) during the time of the Prophet (saw). After he would make adhan, he would stand at the Prophet's door and say, "Hayyah 'alas-salah, hayyah 'alal-falah, the salah O Messenger of Allah." The sweet days with the Prophet (saw) soon came to an end. Everyone in Madinah wept over the death of the dearest man ever on the earth. Bilal was asked to make adhan before the burial of the Prophet. He started the call, "Allahu Akbar ... ", but when he came to the name of the Prophet (saw) he was sobbing so heavily, he could not continue. He said, "By Allah I will not say the adhan anymore."
Bilal asked the Khalifah, Abu Bakr, to allow him to go to ash-Sham for jihad, he spent the rest of his life there. He made adhan only twice since then. The first was when 'Umar came to ash-Sham. The second was when he visited the tomb of the Prophet (saw) in Madinah. Upon hearing his voice, people started to cry for it reminded them of the days of the Prophet (saw) .