What is the stance of Islam on the abolition of slavery?

Slavery is ancient, and Islam regulated the relationship between master and slave. It enjoined masters to treat slaves with kindness, feed them, clothe them, and not burden them with what they cannot bear, as stated in the Almighty's saying: "and those whom your right hands possess," and the Prophet's (peace be upon him) saying: "They are your brothers." Islam also urged slaves to fulfill their master's rights and promised them a double reward. Furthermore, Islam encouraged the manumission and emancipation of slaves, and made the freeing of necks a part of zakat and an expiation for some sins, which indicates Islam's aspiration for freedom.