The Two Kinds of Renting or Hiring:

CR (451) (a) That the subject of the contract is some existing benefits, contrary to someone becoming indebted like hiring an animal or renting a house or some other property. (b) The subject of the contract is a work, which someone owes to perform and is indebted, just as other loans or debts. In (a) if there is time limit, it is not lawful for the worker within this time to work for himself of for someone else for pay or as a volunteer or for JU'ALA. It is not an offense on his part to do the works that are out of the scope of the contract and are not contrary to it like when the contract requires to work during the day and one works at night for oneself or others for pay or no pay or JU'ALA unless such works affect one's performance during the day. If one works during the time the contract requires him, if he works for himself, the other party has the choice to revoke the contract and demand for refund of what he has paid, or approve the contract and demand for the cost of work that the worker has already done for himself or has volunteered for someone else.