It is handed down most briefly in these words (Exodus 24, v. 13[–14]): “Moses rose up, and his minister [Joshua]; and Moses, going up into the mountain of God, said to the ancients: Wait here, till we return to you.”
(col. 101 & top of 102)
…you.” By saying “[till] we return,” he shows that Joshua himself was with him on that mountain of God, and did not remain below with the elders.