From the Epistle of Alexander II, to William of Monasteriolum (from Ivo, Part IX, c. 82)

By the report of many we have learned that you wish to cast away your own wife and to adhere to another, putting forward the occasion of consanguinity. Whence, by apostolic authority, by forbidding we command you that you by no means presume to dismiss this woman whom you now have as wife, or to lead another, until a council of religious bishops has examined that cause itself.

Matrimonial causes pertain to ecclesiastical judges, nor is a marriage rightly entered to be dissolved short of their sentence.