Is the commission you received from the tenant, and that which you will receive from the owner's agent for finding a tenant for a property, lawful or unlawful?

The act of brokerage (simsara) is permissible. It involves mediating between a seller and a buyer, or a lessor and a lessee. It is permissible for the broker to take a fee from both parties or from one of them, provided that it is agreed upon or is customarily practiced. The proof for its permissibility is the Almighty's saying: "And for he who brings it is a camel's load, and I am responsible for it." [Quran 12:72]. There is no consideration for the lessor paying the fee unwillingly if it was agreed upon. There is also no harm in the owner's agent paying the fee from his own money or from his client's money with his permission, as the key is mutual consent and agreement, based on the Prophet's (peace be upon him) saying: "Muslims are bound by their stipulations."