Midrash su Deuteronomio 23:10

“When a camp goes out against your enemies, you shall beware of everything evil” (Devarim 23:10). There should be no levity among you so that you do not incur any liability. From whom should you learn? From Yiftach. What is written about him? “…and he was the son of a harlot…” (Shoftim 11:1) Rabban Shimon ben Gamliel said that she brought her sister-wife into her house, and our Rabbis say that she was really a harlot; and because there was some levity in him all of the people fell upon him. Therefore it is written “you shall beware of everything evil" and “If there is among you a man who is unclean…” These are Israel who became impure through idolatry, as it says “…scatter them afar like a menstruant; 'Go out,' say to it.” (Yeshayahu 30:22) “…he shall go outside the camp…” (Devarim 23:11) that they were exiled to Bavel. “And it shall be, towards evening…”(Devarim 23:12) the evening of the kingdoms, and the Holy One purifies them as it says “…he shall bathe in water…” (ibid.) and it is written “When the Lord shall have washed away the filth of the daughters of Zion…” (Yeshayahu 4:4) “…and when the sun sets…” (Devraim 23:12) When the King Messiah comes of whom it is written “…and his throne is like the sun before Me.” (Tehillim 89:37) “…he may come within the camp” (Devarim 23:12) These are Israel, entering into the Holy Temple. “And you shall have a designated place outside the camp…” (Devarim 23:13) this is the merit of Avraham. R. Pinchas said- “…so that you can go out there,” to Bavel. “And you shall keep a stake in addition to your weapons…” (Devarim 23:14) Nevuchadnezar demanded that they serve an idol and they said “…let it be known to you, O king, that we will not worship your god…” (Daniel 3:18) “…and you shall return and cover your excrement.” (Devarim 23:14) The covering of idolatry that was in Jerusalem. “For the Lord, your God, goes along in the midst of your camp…” (Devarim 23:15) The Holy One will be revealed to them immediately and saved them from the fire. “Therefore, your camp shall be holy…” (ibid.) Afterwards He will sanctify them as it says “And they shall call them the holy people, those redeemed by the Lord…” (Yeshayahu 62:12)

"the ox of your foe": Here we find that idolators are called "foes" to Israel in all instance, as in (Devarim 23:10) "When you go out as a troop against your foes," and (Ibid. 21:10) "When you go out to war against your foes." R. Eliezer says: Scripture here speaks of a proselyte who backslid. R. Yitzchak says: It speaks of an Israelite. Why, then, is he called your foe? If he hit your son or quarreled with you he becomes "your foe" for the moment.

(Devarim 23:10) "When you go out, an encampment against your enemies, then you shall guard yourself against every evil thing." "when you go out, an encampment": When you go out, go out in an encampment (i.e., en masse).