The Institution of the Holy Eucharist
"Brethren, I received from the Lord that which I also delivered to you; that the Lord Jesus on the same night in which He was betrayed took bread; and when He had given thanks, He broke it and said, 'Take eat; this is my Body which is broken for you; do this in remembrance of Me.' In the same manner He also took the cup, after supper saying, 'This Cup is the new covenant in My Blood. This do as often as you drink it, in remembrance of Me.' For as often as you eat this Bread and drink this Cup, you proclaim the Lord's death till He comes.
"Therefore whoever eats this Bread or drinks this Cup of the Lord in an unworthy manner will be guilty of the Body and Blood of the Lord. But let a man examine himself, and so let him eat of the Bread and drink of the Cup. For he who eats and drinks in an unworthy manner, eats and drinks judgment to himself, not discerning the Lord's Body. For this reason many are weak and sick among you, and many sleep. For if we would judge ourselves, we would not be judged. But when we are judged we are chastened by the Lord, that we may not be condemned with the world."
I Corinthians 11:23-32