What is the ruling on someone who swore to his wife, saying: "I divorce you by three divorces, I will not eat anything from you until you go down to Egypt," when the intention behind the oath was to punish her?

The majority of scholars hold that a conditional divorce takes effect when the condition is met. So, if you made the triple divorce conditional upon eating from what your wife cooks until you travel to Egypt, and you ate from it as you intended, then the triple divorce has taken effect according to the majority. Consequently, she becomes unlawful for you until she marries another husband in a valid marriage, and he then divorces her after consummation. However, Sheikh al-Islam Ibn Taymiyyah and those who agreed with him are of the view that only an expiation for breaking an oath (kaffarat yamin) is required if you did not intend divorce but rather intended to discipline your wife. If you did intend divorce, then only a single divorce takes effect.