From the Epistle of John VIII, to Edered, Archbishop of the English, A.D. 877

To those whom you assert to leave their own wives contrary to the precepts of the Lord, we command that neither the man depart from the wife nor the wife from the man, except for the cause of fornication; but if he or she has departed on account of this, to remain unmarried, or to be reconciled mutually to each other. Since the Lord says: what God has joined let man not separate; and therefore, since each cannot desert the former wife joined to him by legitimate matrimony, by no reason is it conceded to him to lead another while the former is living.