What is the ruling on a husband saying to his wife: "I swear by Almighty God three times that you will be divorced if you spend any of your money on the house"?

If the husband intended by this phrasing that he would divorce his wife if she spent from her own money on the house, then if she does spend, he has the choice between divorcing her or offering expiation for the oath.

However, if he intended that the divorce would occur immediately upon her spending, then it is a conditional divorce that takes effect upon her spending. If it was the first or second divorce, he may take her back before the 'iddah (waiting period) expires. If it was the third, she becomes irrevocably divorced from him with a major separation (baynunah kubra), and she is not lawful for him unless she marries another man, who then divorces her or dies, and her 'iddah ends. Sheikh al-Islam Ibn Taymiyyah is of the view that a conditional divorce not intended to effect divorce does not take place, and the one who made the oath is liable for expiation for an oath.