Is it permissible to stipulate in a hiring lease that if the rent is paid on the first of every month, the tenant will receive a discount of $100?

Answer

It is not permissible to add as a condition that you will give them a discount of $100 if they pay on the first of the month. Once you stipulate it as a condition, then the discount becomes binding. The tenant will then demand it. This too is riba. You should merely fix the rent without mentioning discount. If they pay on the first, you may then give them the discount if you so wish. But it must not be fixed as a condition which they can demand.