Hadith 1358
Abu Hurairah (May Allah be pleased with him) reported:
وعن أبي هريرة رضي الله عنه قال: قال لي رسول الله صلى الله عليه وسلم : "من أعتق رقبة مسلمة أعتق الله بكل عضو منه عضوًا منه من النار حتى فرجه بفرجه" ((متفق عليه))
The Messenger of Allah (ﷺ) said, "He who sets free a Muslim slave, Allah will deliver from the fire of Hell every limb of his body in return for every limb of the slave's body, even his private parts." [Al-Bukhari and Muslim].
In plain words
Whoever frees a Muslim slave will have each limb of his own body saved from the Fire in return for a limb of the freed person. Restoring another's freedom becomes a cause of one's own deliverance.
Reference : Riyad as-Salihin 1358 In-book reference : Book 11, Hadith 74