What is the ruling on someone who said to his house, "The house is forbidden to me just as so-and-so is forbidden to me" - referring to his wife with whom he has a marriage contract - and then entered the house?

If the prohibition of the wife is made contingent upon entering the house, then entering the house entails the prohibition, and the preponderant view is that it incurs the expiation of ẓihār. As for prohibiting oneself from entering the house, that falls under the category of prohibiting what is lawful. According to the Maliki and Shafi'i schools, nothing is incurred thereby, whereas the Hanafis and Hanbalis hold that it necessitates an expiation for breaking an oath (kaffārat yamīn).