What is the ruling regarding a man who has intercourse with his wife while she is observing the six days of Shawwal fast, and he is not fasting?

A person observing a voluntary fast is master of himself; he may complete his fast or break it, though completing it is preferable. If a woman observes a voluntary fast without her husband's permission, he may call her to bed, and she is obliged to respond. However, if she fasts with his permission, he may not spoil her fast, but if he desires her, it is better for her to respond to him.