Ibn Jurayj (may Allah have mercy on him) says: I said to Ata' (may Allah have mercy on him): "A mukatab slave belongs to a group of people, and some of them want to make a settlement (muqata'ah) separately?" He said: "No, unless it is the same wealth for all."
Imam al-Shafi'i (may Allah have mercy on him) says: No one should take anything from his mukatab without his partners.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21698