Numbers 9:8

And Moses said unto them, Stand still, and I will hear what the LORD will command concerning you.

Numbers 9 is where the narrative of Exodus resumes, with Israel still encamped at Sinai, as it begins to recount the people's wilderness journeys. The chapter records Israel's first Passover after leaving Egypt, kept during the nearly year-long stay at Horeb. In the verse Moses tells the people to wait while he seeks the Lord's instruction concerning their question, asking God for direction before giving them an answer. Its setting is the Passover observance with its required restrictions, when people avoided defilement from the dead during the ceremonial season.

All the feasts given to Israel occurred annually and were to be observed only at the time when they were due, with the single exception that those who on account of ceremonial uncleanness were unable to keep the Passover in the first month could keep it on the same day of the month in the second month. The only warrant for eating the Passover at a different time was ceremonial defilement, and then it was to be eaten just one month later, not one day before. This proves that Jesus and His disciples ate the Passover at the specified time, not the evening before the regular time, in conformity to Jewish custom and the ceremonial law.