הלכה אויף שמואל א 15:12

The commandment to set up a place in which to defecate: That we were commanded that when our soldiers go out to war that we set up and designate a set place (see Tosefta Megillah 3:15) for the soldier, in which every man can go out to take care of his needs; so that their “needs” not be [found] in every place and between the lodgings, like the [other] peoples do (Sanhedrin 104b). And about this it is stated (Deuteronomy 23:13), “And there shall be a yad for you outside the camp, etc.” And the language of Sifrei is “A yad is always a place, as it states (I Samuel 15:12), ‘and behold, he established a yad.’”