29 In this respect We think fit to point out something which should be carefully borne in mind when mission territory that has been under the care of foreign missionaries is entrusted to a native Bishop and clergy. It is not necessary that the religious institute whose members tilled the mission field with their sweat, should leave it altogether when by decree of the S. Congregation of Propaganda Fide the vineyard, which was cultivated by them and is not flourishing, is handed over to other husbandmen. It will be advantageous and becoming that such a religious institute remain on to cooperate with the newly appointed native Bishop. As in the rest of the Catholic dioceses of the world Religious usually assist the local Ordinary, so in mission countries let them not cease, though foreigners, to labor for the Church in an auxiliary capacity. Thus what the Divine Master proclaimed at the well of Sichar will be happily fulfilled: "And he that reapeth, receiveth wages and gathereth fruit unto life everlasting: that both he that soweth and he that reapeth may rejoice together."
Source: Evangelii Praecones (Vatican.va)