Slavery is a legal or economic system in which people are treated as property. The practice was rampant in pre-Islamic Arabia, but the advent of the faith sought to wipe out the practice. 

Muhammad's^sa efforts to free slaves

Prior to the advent of Islam, slavery was rampant across Arabia. However, Muhammad^sa not only treated slaves kindly but advocated for their freedom and rights:

The Prophet^sa said: Allah said: "I will be an opponent to three types of people on the Day of Resurrection: 1- One who makes a covenant in My Name, but proves treacherous. 2- One who sells a free person and eats his price and 3- One who employs a laborer and takes full work from him but does not pay him for his labour."

- Bukhari

Abu Masud Al-Badri^ra said: "I was beating my slave with a whip when I heard a voice behind me which said: '...Abu Masud! Bear in mind that Allah has more dominance upon you than you have upon your slave."...I said: "He is free for the sake of Allah." He^sa said, "If you had not done this, you would have been singed by the Fire [of Hell]."

- Muslim

For this reason, many of the earliest adherents of Islam were slaves while many of the earliest and fiercest opponents of Islam were slave owners. Muhammad^sa freed every single slave who came into his possession within his lifetime and was able to personally free 63 slaves. Meanwhile the early Muslims were able to free well over 30,000 slaves.

Not only were the slaves freed but Muhammad^sa took special care to ensure the social standing of the slaves was improved and that any stigma associated with their former slavery was removed. For example, Muhammad^sa not only personally freed Zaid bin Harithah, but later appointed him as a chief of the city of Medina and as a commander of the Muslim army. Zaid's son Usama was also given similar roles of responsibility. Moreover, Muhammad^sa arranged Zaid's marriage to his own cousin, Zainab bint Jahash. For a former slave to marry a noble woman in Arabia at that time would have been considered highly abnormal. Muhammad's^sa kind treatment of the former slave was so great that Zaid said he loved Muhammad^sa more than his own father.

In another instance, Muhammad^sa encouraged his companion Abu Bakr to buy the slave Bilal from his cruel owner, for the purpose of freeing Bilal. Abu Bakr freed Bilal, administered medical treatment to heal his injuries, taught him how to read and write and employed him as his store keeper. Bilal was not only a slave but was of African descent, meaning - unlike the fairer Arabs he lived among - he was black. Yet despite the stigma associated with slaves, Muhammad^sa sought to end any form of racial prejudice. Muhammad^sa appointed Bilal the first caller to prayer in Islamic history as well as numerous official roles including managing the state's treasury. The affection shown Bilal by Muhammad^sa led to the former African slave often being revered more greatly than even the Arab chiefs by the early Muslims. Muhammad's^sa desire to raise the status of former slaves was so great that he would say:

Narrated Abdullah bin Amr: I heard the Prophet^sa saying: "Learn the recitation of Quran from four persons: Ibn Masud, Salim, the freed slave of Abu Hudhaifa, Ubai and Muadh bin Jabal."

- Bukhari

The Prophet^sa said, "The best among you are those who learn the Quran and teach it." 

- Bukhari