What is the ruling regarding a man saying to his wife: "You are forbidden to me just as my sister is forbidden to me," intending thereby to abstain from sexual intercourse and not to issue a divorce?

The preponderant opinion is that the prohibition of the wife refers back to the husband's intention. Therefore, this is Dhihar, which is a reprehensible and false statement, and one must avoid it and repent from it. The wife of the one who commits Dhihar becomes unlawful to him until he expiates for his Dhihar.