Gregory VII, pope. [Letter to Matilda of Tuscany, countess of Tuscany, duchess of Lorraine, 1074] in Das Register Gregors VII (Gregorii VII Registrum) ep 1.47

[Letter from Pope Gregory VII to Matilda of Tuscany, countess of Tuscany, duchess of Lorraine]
Gregory discourages Matilda from abandoning the world in order to save her soul. Matilda had apparently asked to have her marriage dissolved so she could take the veil, but Gregory advised her that her work for God in the world was too important. We do not have her thoughts on this, but Anselm's suggests that she had recurring thoughts about a religious life.
Online at Epistolae (See also Bibliographia record).