"But our opinion is in accordance with the Eucharist, and the Eucharist in turn establishes our opinion."

     St. Irenaeus, Adv. haer. IV.xviii.5, as trans. Roberts & Rambaut, ANF 1, 486.  CCC 1327:

Our way of thinking is attuned to the Eucharist, and the Eucharist in turn confirms our way of thinking.

This appears on p. 205 of vol. 2 of the 1857 edition ed. W. W. Harvey (where it is Adv. haer. IV.xxxi.4), as follows (I have not yet checked SC):

Ἡμῶν δὲ σύμφωνος ἡ γνώμη τῇ εὐχαριστίᾳ, καὶ ἡ εὐχαριστία βεβαιοῖ τὴν γνώμην. 

Nostra autem consonans est sententia Eucharistiae, et Eucharistia rursus confirmat sententiam.

The immediate context here is an insistence, against the gnostics, on "the hope of the resurrection [of the flesh] to eternity":  "our bodies, when they receive the Eucharist, are no longer corruptible", but "partake of life".