The Lord spoke to Moses in the tent of meeting in the Wilderness of Sinai, on the first [day] of the second month of the second year after Israel's departure from the land of Egypt:
References for Numbers 1:1
"Take a census of the entire Israelite community by their clans and their ancestral houses, counting the names of every male one by one.
References for Numbers 1:2
You and Aaron are to register those who are 20 years old or more by their military divisions-everyone who can serve in Israel's army.
References for Numbers 1:3
A man from each tribe is to be with you, each one the head of his ancestral house.
These are the names of the men who are to assist you: Elizur son of Shedeur from Reuben;
Shelumiel son of Zurishaddai from Simeon;