On the Mysteries as Sources for Orthodox Doctrine

St. Irenaeus of Lyons died ca. 202

[O]ur opinion is in accordance with the Eucharist, and the Eucharist in turn establishes our opinion. (Against Heresies 4.18.5)

St. Basil the Great ca. 330-379

We believe as we were baptized, and we worship as we have believed. (De Ascetica Disciplina 1, PG 31, 649C)

St. Proper of Aquitaine ca. 390-455

Let us consider the sacraments of priestly prayers, which having been handed down by the Apostles are celebrated uniformly throughout the whole world and in every Catholic Church so that the law of praying might establish the law of believing. (Patrologia Latina 51:209-210)