What is the ruling of Islamic law concerning the failure to fulfill a promise to install a telephone line for a relative, after it became clear that previous promises were based on incorrect information regarding the ownership of the line?

A promise conditioned on entitlement to compensation does not necessitate fulfillment if it becomes clear that the compensation is not due, unless the fulfillment is made as an act of charity. This is more befitting for the affluent, as it fosters harmony and prevents discord, especially if the promised person is a relative.