Exchanging mustard seed for oil

Question

Question: In our area mustard oil is obtained in this way: mustard seed is given to the oil-presser, and after having him press out the oil, oil amounting to a quarter of the mustard is taken from him, even if more oil comes out, and the payment for pressing the oil is the mustard oilcake; or the oil-presser brings oil from his own stock and is given the same amount of mustard. Now it is asked whether any of these forms is permissible or not, and if not, why? Please write in detail with proofs.

Answer

In the first case the lease (ijara) is invalid (fasid). Firstly, because it is not permissible to fix as the hireling's wage something that does not exist at present but will result from the hireling's own work: [ar]ولو دفع غزلًا لآخر لينسجه له بنصفه أي بنصف الغزل، أو استأجر بغلًا ليحمل طعامه ببعضه، أو ثورًا ليطحن بره ببعض دقيقه، فسدت في الكل؛ لأنه استأجر بجزء من عمله، والأصل…

Source: Fatawa Mahmudiyya

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