Slavery in Islam still lawful

From the indefatigable Islam Q&A:

When the question is asked: why does Islam permit slavery? We reply emphatically and without shame that slavery is permitted in Islam, but we should examine the matter with fairness and with the aim of seeking the truth, and we should examine the details of the rulings on slavery in Islam, with regard to the sources and reasons for it, and how to deal with the slave and how his rights and duties are equal to those of the free man, and the ways in which he may earn his freedom, of which there are many in sharee’ah...

Islam limited the sources of slaves that existed before the beginning of the Prophet’s mission to one way only: enslavement through war which was imposed on kaafir prisoners-of-war and on their womenfolk and children.

Shaykh al-Shanqeeti (may Allaah have mercy on him) said: The reason for slavery is kufr and fighting against Allaah and His Messenger. When Allaah enables the Muslim mujaahideen who are offering their souls and their wealth, and fighting with all their strength and with what Allaah has given them to make the word of Allaah supreme over the kuffaar, then He makes them their property by means of slavery unless the ruler chooses to free them for nothing or for a ransom, if that serves the interests of the Muslims. End quote from Adwa’ al-Bayaan (3/387).