Treatise XIII. On Confirmation

Confirmation is a sacrament of the new law, by which through the anointing of chrism, under a certain form of words, there is given to the baptized the fullness of the Holy Spirit for firmly believing and for intrepidly confessing the faith.

It is indeed clear that Confirmation is truly and properly so called a sacrament and distinct from Baptism; but it is not clear concerning the time in which it was instituted. The more probable opinion is that it was instituted after the resurrection. According to others, Christ instituted the Sacrament of Confirmation at the Last Supper after the institution itself of the Eucharist. - Cf. De Augustinis, Thesis 1, p. 410.