On the fourteenth day of this month at twilight, you shall keep it at its appointed time; according to all its statutes and ordinances you shall keep it.”
On the first day [of the festival] of Unleavened Bread, when [as was customary] they sacrificed the Passover lamb, His disciples asked Him, “Where do You want us to go and prepare for You to eat the Passover?” [Matt 26:17-19; Luke 22:7-13]
Then came the preparation day of Unleavened Bread on which the Passover lamb had to be sacrificed. [Ex 12:18-20; Deut 16:5-8; Matt 26:17-19; Mark 14:12-16]