Abu Mu'ammal (may Allah be pleased with him) was the man who was the first to make a contract of manumission (mukatabah) in Islam, in the time of the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) said: "Help Abu Mu'ammal." So I was helped; I was given so much wealth that after (paying) the contract of manumission something was left over, and he (peace and blessings be upon him) said: "Spend it in the path of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الصدقات / 13191
The narrator says: I went on a Friday, and a slave with a contract of manumission (mukatab) came to Sayyiduna Abu Musa (may Allah be pleased with him). The narrator says: He was the first beggar I had seen. He said: I am a hard-pressed person with a contract of manumission. He (Abu Musa) urged the people and helped him. Then clothes and dirhams began to be given to help him, until he said: This is enough for me. He went to his masters and they settled his contract of manumission, and three hundred dirhams were left over with him. He came to Sayyiduna Abu Musa (may Allah be pleased with him) and asked, and he said: Spend them on people like yourself.
We have narrated a similar story from Sayyiduna Ali (may Allah be pleased with him), that he said: Spend them on those with contracts of manumission.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الصدقات / 13192