Is it permissible to swear, using the phrase "By what is unlawful, I will not go until she comes," with the intention of severing ties of kinship?

A Muslim should avoid excessive swearing, especially if it is by other than Allah, or for a sin or severing ties of kinship. In the case of swearing by that which is forbidden, scholars have differed regarding its ruling. Some have favored the obligation of kaffarat al-dhihar (expiation for dhihar), which is freeing a slave, or fasting for two consecutive months, or feeding sixty needy persons. Therefore, if the maternal uncle breaks his oath and visits his sister, he must offer kaffarat al-dhihar. Both parties are advised to reconcile and maintain ties of kinship, and the sister is urged to visit her brother to alleviate the burden of the oath.