Gregory IX, Pope. [Letter to Agnes of Prague, 1237] in Bullarium Franciscanum Romanorum Pontificum 1.213

[Letter from Pope Gregory IX to Agnes of Prague]
The pope, praising Agnes's choice of life and devotion to that choice, grants her request to be present in the choir for the celebration of the mass and the consecration of the Eucharist.
Online at Epistolae (See also Bibliographia record).