Joshua 22:10, 34

And when they came unto the borders of Jordan, that are in the land of Canaan, the children of Reuben and the children of Gad and the half tribe of Manasseh built there an altar by Jordan, a great altar to see to.

And the children of Reuben and the children of Gad called the altar Ed: for it shall be a witness between us that the LORD is God.