The Quran has abolished slavery!
The Quran used a two-stage method to abolish slavery that existed in the society in which it was revealed:
A) DRYING UP THE SOURCE OF SLAVERY
• “Release them free (prisoners of war) either without compensation or with ransom.” (The Quran, Muhammad [47] 4). For example, some of the prisoners of the Battle of Badr were released in exchange for teaching ten Muslim children to read and write. Prisoners of war may not be made slaves or concubines.
• “Free the slave/remove every yoke (Fakku Raqaba).” (The Quran, al-Balad [90] 13). Anyone who does not follow this command will face fire (verse 20). For example, Abu Bakr saved Bilal by giving a fortune to fulfill the requirements of this verse. Today there are no longer any slaves, but there are, for example, people who, despite good intentions, go to prison because of their debts or there are people who are forced to work like slaves out of necessity. They also need to be saved.
B) DISCONTINUE EXISTING SLAVES OVER TIME
The Quran freed the slaves that existed at that time not all at once, but through various occasions, depending on a process. One of the punishment options for some crimes is the freeing of slaves:
Killing people accidentally (The Quran, an-Nisa [4] 92).
Az-Zihar (The Quran, al-Mujaadila [58] 3).
Breaking an Oath (The Quran, al-Maida [5] 89).
Again, some of the eight groups of people to whom zakah and alms are given are those who want to be freed from slavery (The Quran, at-Tawbah [9] 60).
Slaves / concubines can be freed through marriage, provided that this occurs with their consent (The Quran, al-Baqara [2] 221; an-Nisa [4] 3, 25; an-Nour [24] 32).
Unfortunately, the Muslim tradition has allowed slavery by either perverting or ignoring the verses. The last country in the world to abolish slavery was the Islamic Republic of Mauritania (1981).
As a result, the Quran ensured that the existing slaves were freed after a process. Islam abolished slavery by drying up the purchase of new slaves.