What is the ruling on subletting if the original tenant's contract with the landlord stipulates that this is not allowed, and does the sin fall only on the original tenant, or on both him and the subtenant?

The answer is summarized as follows: Subleasing the rented property without the landlord's knowledge is a matter of dispute among scholars. Some stipulate that the landlord must not have conditioned the tenant to utilize the benefit himself exclusively. This condition and the validity of the contract alongside it are subject to disagreement: some do not validate the contract, some validate it and nullify the condition, and some validate both. The preponderant opinion is that the tenant is not permitted to sublease the property to another if the landlord stipulated against it, and it is not permissible for one who knows of this condition to sublease from the tenant.