Does a divorce take effect if a man tells his wife: "If you send money to your family without my knowledge, you remain divorced," and then he himself later transfers the amount, knowing that his intention was merely to threaten?

It is not permissible for the wife to give gifts to her family from her husband's money unless he gives her permission, because the Prophet (peace and blessings of Allah be upon him) said: "Every Muslim's blood, wealth, and honor are sacred to another Muslim." However, if she gives a gift from her own money, there is no harm in it, and she does not need her husband's permission, except according to the Malikis and Tawus if the amount exceeds one-third.

Regarding conditional divorce, if you intended that the money should not reach the wife's family by any means, then the divorce has occurred because you broke your oath. However, if you intended that the divorce would not occur unless the wife sent the gift herself without your knowledge, or if you had no specific intention, then the divorce does not occur if you were the one who transferred the gift. An oath is based on the intention of the one who makes it. It is advisable to avoid swearing by divorce.