Pope Paul VI
Sacerdotalis Caelibatus §77
Sacerdotalis Caelibatus: On the Celibacy of the Priest
77 Rightly jealous of his full self-giving to the Lord, the priest should know how to guard against emotional tendencies which give rise to desires not sufficiently enlightened or guided by the Spirit. He should beware of seeing spiritual or apostolic pretexts for what are in fact dangerous inclinations of the heart.
Source: Sacerdotalis Caelibatus (Vatican.va)