Tradition
St. Cyril of Jerusalem
Catechetical Lectures
Book 22 › Introduction
(On the Mysteries. IV.)
On the Body and Blood of Christ.
1 Corinthians 11:23
I received of the Lord that which also I delivered unto you, how that the Lord Jesus, in the night in which He was betrayed, took bread, etc.
Source: Catechetical Lectures (New Advent)