Canon XXI
A bishop may not be translated from one parish to another, either intruding himself of his own suggestion, or under compulsion by the people, or by constraint of the bishops; but he shall remain in the Church to which he was allotted by God from the p. 119 beginning, and shall not be translated from it, according to the decree formerly passed on the subject.
A bishop even if compelled by the people, and compelled by the bishops, must not be translated to another diocese.
See the treatment of the translation of bishops in the Excursus to canon xv. of Nice.
Compare this canon with Apostolical Canon number xiv.
This canon is found in the Corpus Juris Canonici, Gratian’s Decretum, Pars II., Causa VII., Quæst. I., can. xxv., from Isidore’s version.