The Shiite website, Al-Islam says:
He also felt pity for the poor man He told Abu Bakr to purchase Bilal from Ummayya and set him free. This was done.
We read in the same website
Most of the early converts to Islam were “poor and weak.” But there were a few rich Muslims also like Hudhayfa bin Utba and Arqam bin Abil-Arqam. And all those men whom Abu Bakr brought into Islam – Uthman, Talha, Zubayr, Abdur Rahman ibn Auf, Saad ibn Abi Waqqas and Abu Obaidah ibn al-Jarrah – were also rich and powerful. They were members of the various clans of the Quraysh.
Bilal, the Ethiopian slave of Umayya bin Khalaf. Umayya and other infidels tortured him in the savage glare of the torrid sun of Makkah, and they tortured him beyond the limits of human endurance. But he was fortified by inner sources of strength and courage which never failed him. Love of God and the love of His Messenger made it possible for him to endure torture with cheer. Abu Bakr bought him from his master and set him free. When the Apostle migrated to Medina, he appointed Bilal the first Muezzin of Islam.
Abu Fukaiha was the slave of Safwan bin Umayya. He accepted Islam at the same time as Bilal. Like Bilal, he was also dragged by his master on hot sand with a rope tied to his feet. Abu Bakr bought him and emancipated him. He migrated to Medina with the Prophet but died before the battle of Badr.
Lubina was a female slave of Mumil bin Habib. Amin Dawidar writes in his book, Pictures From the Life of the Prophet (Cairo, Egypt, 1968), that Umar bin al-Khattab, the future khalifa of the Muslims, tortured her, and whenever he paused, he said: “I have not stopped beating you out of pity. I have stopped because I am exhausted.” He resumed beating her after he had rested. Abu Bakr bought her and set her free.
Zunayra was another female slave. When she declared her faith in Islam, Umar ibn al-Khattab, and Abu Jahl, took turns in torturing her until she became blind. Amin Dawidar states that many years later she recovered her sight, and the Quraysh attributed this recovery to the “sorcery” of Muhammad. Abu Bakr bought her and set her free.
Nahdiyya and Umm Unays were two other female slaves who became Muslims. Their masters tortured them for accepting Islam. Abu Bakr bought them and gave them their freedom.