It is going to elaborate the Islamic and quranic teachings briefly on slavery explaining that the terrorist and Takfifiri groups' behavior with the arrested people is not Islamic.
Whereas the terrorist groups such as ISIS practice the slavery capturing the innocent Muslim and non-Muslim civilians as slaves, Islam as the most perfect divine religion established a new social and economic system through which slaves respected and dignified in order to become free. So, the main purpose of Islam is to break the ancient rule of slavery and not to continue treating human as slaves selling or buying them in bazar.
In Badr battle the prophet Muhammad (P) ordered his companions to free some of the captives on ransom (in form of money or work like teaching ten Muslim children how to read and write), and some of them without any ransom.[1] “…..to let the captives go free, either with or without any ransom" [2] As it is mentioned in the verse of the holy Quran prophet and his followers can liberate the captives without any kind of ransom, it proves that practicing slavery is not obligatory according to the holy Quran and Islamic sharia.
When the holy Quran commands Muslim not to keep the captives rather they can be freed without any sort of ransom. It shows that Islam opposes slavery basically but the problem is that it is impossible to fulfill the new rules once or in one day. Slavery was a very old and ancient tradition, which was impossible to be changed in a very short time. Islam tried to change this tradition gradually by making different rules with regard to slaves and their freedom.
Finally, it must be mentioned that slavery is categorically forbidden nowadays across the globe including the Islamic countries. But the question is that why the terrorist groups such as ISIS, backed by the western powers, practice slavery capturing the poor people of Iraq and Syria then selling them in bazar like the people of the past time. It is clear that such groups try to present and distorted and misleading picture of Islam maintaining abolished tradition of slavery.
Notes:
[1] Ibn Sa'd, al-Tabaqatul Kabir, Vol. II: 1 (Leiden: E.J. Brill, 1912), pp.11, 14.
[2] Chapter Muhammad, verse 4. فَشُدُّوا الْوَثَاقَ فَإِمَّا مَنًّا بَعْدُ وَإِمَّا فِدَاء حَتَّى تَضَعَ الْحَرْبُ أَوْزَارَهَا.