Is the husband's statement to his wife, "You are forbidden if you spend a single pound in this house," considered a divorce? And is their marital intimacy after that considered adultery? And what are the consequences for them?

The preponderant opinion is that if a husband makes a prohibition conditional on his wife spending some of her money on the household, and a breaking of that oath ensues, the ruling depends on the husband's intention with the prohibition. If he intended divorce, it is a divorce. If he intended ẓihār, it is ẓihār. If he did not intend divorce or ẓihār, then he must pay kaffārat yamīn (expiation for breaking an oath) if he breaks it, and it does not result in divorce or ẓihār.

Therefore, the husband should directly consult knowledgeable and pious scholars so that they may inquire about his intention behind what he uttered and then issue a fatwa based on that. It is important to note that threatening with prohibition or divorce is an unsound approach and may lead to undesirable consequences.