פירוש על קידושין 99:11

In this case, the man does not go to Israel, and the question again arises, whether he can renege on his sale. According to the first version, he could have gone and since he did not, the sale cannot be annulled. According the second version, where R. Ashi responds in the form of a question, if some unforeseen circumstance, something that could not be helped, prevents him from moving to Israel, then he can renege on the sale.