Is he who swore not to commit a certain sin—saying that if he were to commit it, Allah would take his son—then committed it, sinful?

If a swearer breaks his oath, expiation for the oath becomes obligatory upon him. This expiation is feeding ten needy persons, or clothing them, or freeing a slave. If he cannot find any of these, then he must fast for three days, based on the Almighty's saying: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [each of them] - then a fast of three days. That is the expiation for oaths when you have sworn." What was mentioned about Allah taking the son if the sin is committed has no relation to expiation, because that is solely in the hand of Allah.