Sahih al-Bukhari Book 49, Hadith 2
I asked the Prophet, "What is the best deed?" He replied, "To believe in Allah and to fight for His
Cause." I then asked, "What is the best kind of manumission (of slaves)?" He replied, "The
manumission of the most expensive slave and the most beloved by his master." I said, "If I cannot
afford to do that?" He said, "Help the weak or do good for a person who cannot work for himself." I
said, "If I cannot do that?" He said, "Refrain from harming others for this will be regarded as a
charitable deed for your own good."
The Prophet (ﷺ) said, "Whoever frees a Muslim slave, Allah will save all the parts of his body from the (Hell) Fire as he has freed the body-parts of the slave." Sa`id bin Marjana said that he narrated that Hadith to `Ali bin Al-Husain and he freed his slave for whom `Abdullah bin Ja`far had offered him ten thousand Dirhams or one-thousand Dinars.
The Prophet (ﷺ) ordered us to free slaves at the time of solar eclipses.