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), 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 (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) and must be annulled. The lessee would then be entitled to the customary rent (ujrat al-mithl) for the past period.