What is the ruling on working to serve a cow in exchange for half of its produce, while the ownership of the cow remains with its original owner?

This contract is a lease contract (ijarah (definition)), and it is not permissible for the rent to be a portion of the cow's produce (half or a quarter) due to the presence of gharar (definition) (uncertainty) and jahalah (ignorance). The Prophet, peace and blessings be upon him, forbade gharar and hiring a worker until his wage is clearly specified. The cow might not produce, or it might die before producing, which makes the contract impermissible due to the lack of a known, specified rent.

If the contract is concluded in this manner, it is invalid (fasid (definition)) and must be annulled. The lessee would then be entitled to the customary rent (ujrat al-mithl) for the past period.