Is the intention not to perform an obligation considered a sin if its performance becomes impossible due to divine decree and destiny?

If a person intends to abandon an obligation before its due time, and then a legitimate impediment prevents him from fulfilling it, there is no sin upon him. However, if he intends to abandon it after its due time has begun, and then a legitimate impediment prevents him, he incurs sin, because one of the conditions for delaying an open-ended obligation (wajib muwassa') is the firm intention to perform it. Another condition for delaying an open-ended obligation is the strong presumption of a safe outcome until the delayed act is performed. The soundest view is that it is obligatory to firmly intend to perform an open-ended obligation upon the arrival of its due time; otherwise, one incurs sin.