Hasan ibn Ali (May Allah be pleased with him), was the grandson of our Prophet ﷺ. Once his slave walked into the gathering of Abu Huraira (May Allah be pleased with him) where he was narrating Ahadeeth. One of the hadith that settled in the heart of the slave was:

"If somebody manumits a Muslim slave, Allah will save from the Fire every part of his body for freeing the corresponding parts of the slave's body, even his private parts will be saved from the Fire) because of freeing the slave's private parts."

Sahih Bukhari: 6715

The slave happily memorised the hadith and when he went back, he reported to his master Hasan (May Allah be pleased with him) and said, “I attended the sermon of Abu Huraira (May Allah be pleased with him) and he was narrating beautiful narrations of your grandfather ( the Prophet ﷺ ) and one of them was:

"If somebody manumits a Muslim slave, Allah will save from the Fire every part of his body for freeing the corresponding parts of the slave's body, even his private parts will be saved from the Fire) because of freeing the slave's private parts."

Hasan (May Allah be pleased with him) got up and both of them went to Abu Huraira (May Allah be pleased with him) and confirmed the narration from him. When it was confirmed, Hasan (May Allah be pleased with him) looked at him and said, “You heard many Ahadeeth but remembered only the one that suited your need, so go! I have set you free for the sake of Allah.”

 There are narrations that state many of the Companions set their slaves free with a hope of being pardoned by Allah. There are different ways to set the slaves free.

1. For getting a reward from Allah
2. Mudabbar
3. Mukatab

Mudabbar is a clause where a master informs that after he dies, his slave should be set free. In mukatab, a slave is set free if he fulfils the conditions set by his master. It may be a sum of money. Under such a condition, if someone uses his wealth to set the slave free, he would be highly rewarded by Allah.  Islam as a religion has encouraged his followers to treat slaves kindly, respect them as humans, and to set them free in hope of receiving rewards from Allah.