מדרש על בראשית 32:13

And he hid him in the sand (ibid., v. 12). He said to the Israelites: You are likened to sand,¹²Referring to Thy seed as the sand of the earth (Gen. 32:13). which moves soundlessly from one place to another; so, too, no word of this must depart from your mouths. Therefore it is written: And he hid him in the sand (ibid.).