Council of Trent: Session VI, Reformation, Chapter V

CHAPTER V. Bishops shall neither exercise any pontifical function, nor ordain, in another diocese.

It shall not be lawful for any bishop, under the plea of any privilege soever, to exercise pontifical functions in the diocese of another, save by the express permission of the Ordinary of the place, and in regard to those persons only who are subject to that same Ordinary: if the contrary shall have been done, the bishop shall be ipso facto suspended from the exercise of episcopal functions, and those so ordained (be similarly suspended) from the exercise of their orders.

Translation: J. Waterworth, The Canons and Decrees of the Council of Trent (1848), Hanover Historical Texts Project transcription (1995).