Harun bin Antarah narrated from his father that he said: I was present with Ali and Uthman (may Allah be pleased with them both); both of them used to give provision to people's slaves.
It is possible that they both gave their masters what suffices them and what suffices their slaves whom they cannot do without, and Zayd's slave was given because of the help he provided.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12985