The Quran has abolished slavery!
The Quran has definitely abolished slavery. There is no permission in the Quran, that allows to make slaves of prisoners of war. Conversely, the 4th verse of the surah Muhammad, which was revealed before the battle of Badr, orders to release prisoners of war with cost (money) or without it. The Quran doesn’t give muslims any other option. Prophet Muhammed never made anyone a slave. According to this same verse, prisoners of war could be taken only, if the enemy collapses strategically. There’s no opportunity to take prisoners before or after the war. However, the madhabs gave permission to continue slavery!
The Quran orders to make a contract of (mukataba) with the slaves, who want to make a payment (fidyah) to be free (al-Nour 24:33). The muslims should prepare for them a fund from the zakah gainings (at-Tawbah 9:60). Furthermore these prisoners should be released for the reason of religious donation (kaffara) or to marry them (al-Nour 24:32). According to al-Baqarah 2:177 to liberate a slave is an appearance of taqwa, but nowadays millions of people are used to working like slaves under different names.
The purpose was to give the slaves their freedom not at once, but slowly with different matters. Otherwise if the slaves were to be released all at once, thousands of them would be thrown into devastation. In fact, after the US civil war during 1861-1865 hundreds and thousands of slaves got their freedom in one night, but they were thrown into a terrible situation, unemployment, homelessness and starvation.
Therefore the Quran states to slowly release the current slaves at the time of the Prophet, and forbids to take new slaves. Slavery had obviously been abolished with the 4th verse of the Surah Muhammad!