Numbers 9:3-5

MSB(i) 3 You are to observe it at the appointed time, at twilight on the fourteenth day of this month, in accordance with its statutes and ordinances.” 4 So Moses told the Israelites to observe the Passover, 5 and they did so in the Wilderness of Sinai, at twilight on the fourteenth day of the first month. The Israelites did everything just as the LORD had commanded Moses.