Numbers 10:10-14

Also on the day of your joy and at your appointed feasts, and on the first days of your months, you shall blow the trumpets over your burnt offerings, and over the sacrifices of your peace offerings; and they shall be as a reminder of you before your God. I am the Lord your God.” The Tribes Leave Sinai

Now in the second year, in the second month, on the twentieth of the month, the cloud was lifted from above the tabernacle of the testimony;

and the sons of Israel set out on their journeys from the wilderness of Sinai. Then the cloud settled in the wilderness of Paran.

So they moved on for the first time in accordance with the command of the Lord through Moses.

The flag of the camp of the sons of Judah, by their armies, set out first, with Nahshon the son of Amminadab, over its army,