What is the ruling on one who swears not to have conjugal relations with his wife for a month?

If a man swears an oath to abstain from conjugal relations with his wife for a period less than four months, he has two options:

1. He can fulfill his oath and not engage in intercourse with her until the period ends. In this case, there is no consequence for him.

2. He can engage in intercourse with her before the period ends, in which case an expiation for breaking an oath becomes obligatory upon him. This expiation is: feeding ten needy persons, or clothing them, or freeing a slave. If he is unable to do so, then he must fast for three days, as Allah (the Exalted) says: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families, or clothing them, or freeing a slave. But whoever finds not [the means] - then a fast of three days. That is the expiation for your oaths when you have sworn" [Al-Ma'idah: 89].

As for one who swears an oath to abstain from conjugal relations with his wife for four months or more, he is considered a muli (one who has taken an oath of abstinence).