the first day. The eating of the Passover took place on the fourteenth of Nisan. See Exo_12:6, Exo_12:8, Exo_12:18. Lev_23:5. Num_9:3; Num_28:16. The fifteenth was the high sabbath, the first day of the feast. See Num_28:17.
Where . . . ? This question shows that the date was the fourteenth of Nisan.