From the Council of Toledo, A.D. 683

Canon V. It will be lawful for no one to lead the surviving queen into marriage for himself, or to stain her by sordid contacts. This will not be lawful for future kings; it will not be permitted to any human being. But if anyone has presumed to do any such thing, whether by coupling to himself the surviving queen in marriage after the death of the deceased prince or by contaminating her with adulterous pollution, whether he is king or any human being, whoever has presumed to violate the sentence of this our sanction, let him be excluded from all communion of Christians, and let him be handed over with the devil to be burned by sulphurous fires.

The same decree was confirmed in the third Council of Zaragoza, A.D. 691, Canon V, with a decree added that the same surviving queen should put off secular dress, assume the habit of religion, and immediately be assigned to a convent of virgins.