Targum for Numbers 2:10

(By) the standard of the camp of Reuben they, shall encamp southward by their hosts, spreading over four miles. And his standard shall be of silk, of three colours, corresponding with (those of) the precious stones that are in the breastplate, azmorad, sapphire, and adamant: on it shall be expressed and set forth the names of the three tribes of Reuben, Shemeon, Gad; and in the midst of it be written, Hear, Israel, the Lord our God is One; and upon it shall be set forth the figure of a stag. Some would have thought there should have been upon it the figure of a young ox; but Mosheh the prophet altered it, that the sin of the calf might not be remembered against them. And the Rabba set over the host of the tribe Reuben was Elizur bar Shedeur.