From the Last Work on the Passover. (Quoted in the Paschal Chronicle.)

Accordingly, in the years gone by, Jesus went to eat the passover sacrificed by the Jews, keeping the feast. But when he had preached He who was the Passover, the Lamb of God, led as a sheep to the slaughter, presently taught His disciples the mystery of the type on the thirteenth day, on which also they inquired, "Where wilt Thou that we prepare for Thee to eat the passover?" ¹ It was on this day, then, that both the consecration of the unleavened bread and the preparation for the feast took place. Whence John naturally describes the disciples as already previously prepared to have their feet washed by the Lord. And on the following day our Saviour suffered, He who was the Passover, propitiously sacrificed by the Jews.