Where in the Bible can you find the institution of the Eucharist?

Answer

All of St. John chapter 6 of the New Testament features Christ declaring that people must partake of His flesh and blood which He will give to them. Christ's Words are such that the people take His meaning literally and indeed Christ is adamant, encouraging this literal interpretation even when some of His own disciples depart. The apostles themselves know this is no parable, often they ask Christ to expound parables He has told the crowd, but their reaction this time is one that takes his Words literally as well. They realize what He has said is impossible and revolting, yet they respond with Faith that He will reveal how this will be done. The manner by which Christ will fulfill His Words is found at the Last Supper, when Christ again references His Body and Blood but reveals them to be present in the Bread and Wine used in the Pasch ceremony. Christ is here instituting the sacrifice of the New Law and His declarative Words are Words of consecration. You can find this institution in full context within the Gospels: St. Matthew chapter 26, St. Mark chapter 14, and St. Luke chapter 22. Even St. Paul speaks of it in 1 Corinthians 11:27-29. The Catholic Church uses these exact Words and actions of Jesus which He commissioned his disciples, the leaders of His Church, to do also in order to enact this same sacrament every time the sacrament is celebrated.