Abu Layla al-Kindi says that a slave wished to make a contract of manumission (mukatabah) with Sayyiduna Salman al-Farisi (may Allah be pleased with him). Sayyiduna Salman (may Allah be pleased with him) asked him: Do you have anything? He said: No. Sayyiduna Salman al-Farisi (may Allah be pleased with him) asked: Then where will you get it from? He replied: By begging from people. Sayyiduna Salman al-Farisi (may Allah be pleased with him) refused to make the contract with him and said: You would feed me the filth of people.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21614