The First Council of Nicaea (325 AD)

If any presbyters have been advanced without examination, or if upon examination they have made confession of crime, and men acting in violation of the canon have laid hands upon them, notwithstanding their confession, such the canon does not admit; for the Catholic Church requires that [only] which is blameless.

Ancient Epitome of Canon IX.

Whoever are ordained without examination, shall be deposed if it be found out afterwards that they had been guilty.

The crimes in question are those which were a bar to the priesthood—such as blasphemy, bigamy, heresy, idolatry, magic, etc.—as the Arabic paraphrase of Joseph explains. It is clear that these faults are punishable in the bishop no less than in the priest, and that consequently our canon refers to the bishops as well as to the πρεσβύτεροι in the more restricted sense. These words of the Greek text, “In the case in which any one might be induced, in opposition to the canon, to ordain such persons,” allude to the ninth canon of the Synod of Neocæsarea. It was necessary to pass such ordinances; for even in the fifth century, as the twenty-second letter to Pope Innocent the First testifies, some held that as baptism effaces all former sins, so it takes away all the impedimenta ordinationis which are the results of those sins.

Some say that as baptism makes the baptized person a new man, so ordination takes away the sins committed before ordination, which opinion does not seem to agree with the canons.

This canon occurs twice in the Corpus Juris Canonici. Decretum Pars I. Dist. xxiv. c. vij., and Dist. lxxxj., c. iv.