If at the time of taking the oath it is possible for one to...

If at the time of taking the oath it is possible for one to fulfil it but afterwards he becomes unable to fulfil it, then his oath becomes annulled from the time he became unable to fulfil it. The same applies if fulfilling the oath becomes so excessively difficult (mashaqqah) for him that he cannot endure what it takes to fulfil it.

If him not being able to fulfil the oath was due to his own free actions, or it was not due to his own free actions but he did not have a legitimate excuse (ʿudhr) for delaying the fulfilment of the oath when he was able to fulfil it, then he will have sinned and kaffārah is obligatory for him.