What is the ruling on throwing money in the trash after swearing to do so with the intention of discipline, and can it be spent instead of thrown away? What is the duration of the oath during which the money must be disposed of? Is it permissible to retract an oath and pay expiation? And what about a previous oath whose wording is not remembered and in which there was no "insha'Allah" exception?

Your oath is binding upon reducing the money you possess. If you do what fulfills this intention, you have honored your oath. Throwing money in the trash is not considered fulfilling the oath because it is a destruction of wealth without right, and the intention behind an oath takes precedence over the literal wording. If you do not reduce the money, you have broken your oath, and an expiation for breaking an oath is incumbent upon you (feeding ten poor persons, or clothing them, or freeing a slave; if you cannot find any of these, then fasting for three days). It is best to hasten to fulfill your oath as long as you possess the money. You cannot retract your oath after breaking it. If you are certain of having broken an old oath, expiation becomes binding upon you, but if you are in doubt, nothing is incumbent upon you.