What is the ruling on selling leased gas cylinders while continuing to pay their monthly rent to the owner, with the intention of returning new cylinders to him in the future upon request?

The tenant's action of selling the leased cylinders is a prohibited aggression and an invalid sale because the tenant does not own the item nor is he authorized to sell it. A sale is only valid when conducted by an owner or someone authorized by them. The tenant must retrieve the cylinders and return them to their owner if possible; otherwise, he must replace them with similar ones. Since the tenant damaged the cylinders by selling them, the lease has been terminated, and he is liable for the leased item, while the previous rent remains due to the lessor. He is also liable for the equivalent rent for the subsequent period, as the cylinders are intended for exploitation.