II.5. On priests.
[...]
(14) [...] However, the Law itself testifies that anyone who has been corrupted after baptism by some mortal sin is not to be promoted to ordination. For in the Law, Moses ordered the priests that no spoiled animal be offered at the altar of God. Afterwards, the priests the Israel rejecting this, God reproached them through Malachi, saying: "O priests, who despise my name. You say, 'How have we despised your name?' By offering polluted food on my altar... And when you offer those that are lame or sick, is that not wrong?" [Mal 1:6-8]. Whence also in Numbers a red heifer, whose ashes are an expiation of the people, is not to be ordered to be offered at the altar of the Lord unless it has not done earthly works and has not borne the yoke of transgression, nor been hindered by the chains of sins [see Num 19:2]. (15) And what more can I bring up? If anyone who has already been placed in the episcopate or presbyterate should admit some mortal sin, let him be withdrawn: would it not be better [if someone] were found to be a sinner before ordination that if he were ordained? For that reason, since the law removes sinners from priesthood, let each one of them consider for themselves and, knowing that "the mighty shall be mightily put to the test" [Wis 6:7 (Vulgate)], withdraw themselves from it not because of the honor but because of the burden, and not go around occupying the place of others who are worthy.
(trans. Knoebel 2008: 75)