Ibn Jurayj (may Allah have mercy on him) says: I said to Ata' (may Allah have mercy on him): Is it obligatory upon me to make a contract of manumission (mukatabah) with him if I know that there is good in him? He said: I consider it nothing but obligatory. Amr bin Dinar (may Allah have mercy on him) also said the same. And I said to Ata' (may Allah have mercy on him): Do you narrate this from anyone? He said: No.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21616