John XIII, Pope. [Letter to Gerberga, abbess of Gandersheim, 968] in Patrologiae cursus completus. Series Latina (Patrologia Latina) 135: 959-60

[Letter from Pope John XIII to Gerberga, abbess of Gandersheim]
This letter takes the monastery under apostolic protection, a conventional procedure which would not ordinarily be included except that it mentions the special circumstances of the request made by the emperor and his son in person.
Online at Epistolae (See also Bibliographia record).