What is the ruling regarding a man telling his wife: "You are forbidden to me as long as I live," intending intercourse, then a minute later amending his statement to make it for a month?

If a man intends, by declaring his wife unlawful, to abstain from conjugal relations with her, either permanently or temporarily, this is disliked (makrooh) but she does not become unlawful to him, and he is obligated to offer an expiation for a broken oath (kaffarat yameen). This is the view of the Shafi'is, who hold that if someone declares his wife unlawful and intends to prohibit her person or sexual intercourse with her, she does not become unlawful to him and he must offer an expiation for a broken oath, even if he does not engage in intercourse. The same applies if he declares her unlawful without any specific intention.