What is the basis for permitting the exchange of labor for specified, but unspecified in amount, food and clothing?

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The evidence supporting permissibility is the narration from Ibn Majah regarding Musa hiring himself out for eight or ten years for the chastity of his private parts and the food for his belly, and the practice of the Companions without objection being considered consensus. Furthermore, since it is established for the wet nurse by explicit text, it can be established for others by analogy. It is compensation for a benefit, allowing custom ('urf) to stand in place of explicit specification, akin to the wife's maintenance or the known amounts of food in expiations (kaffarat).