Numbers 31:19

“And do ye abide without the camp seven days. etc.] Which was the time that anyone that touched a dead body remained unclean, (<041911>Numbers 19:11), whosoever hath killed any person; as most of them if not all must have done; all the males of Midian that fell into their hands being slain by them, that were men grown: and whosoever hath touched any slain; as they must to strip them of their garments, and take their spoil from them: purify both yourselves and your captives, on the third and on the seventh day; which were the days appointed for the purification of such that were polluted by touching dead bodies, (<041911>Numbers 19:11) and their captives, which were the female little ones;…”

“abide without the camp seven days: whosoever hath killed any person . . . purify both yourselves and your captives--Though the Israelites had taken the field in obedience to the command of God, they had become defiled by contact with the dead. A process of purification was to be undergone, as the law required (Lev 15:13; Num 19:9-12), and this purifying ceremony was extended to dress, houses, tents, to everything on which a dead body had lain, which had been touched by the blood-stained hands of the Israelitish warriors, or which had been the property of idolaters. This became a standing ordinance in all time coming (Lev 6:28; Lev 11:33; Lev 15:12).”

“31:19-24 Israelite warriors who had contact with corpses subjected themselves and their equipment to routine, but important, purification rituals (see 5:1-4; 19:1-22).”

“abide: Though the Israelites had acted by the commission of God, yet they had contracted pollution by touching the dead; and the spoil having been used by idolaters, must also be purified in the prescribed manner. Num 5:2, Num 19:11-22; Ch1 22:8 Numbers 31:20”

“Purification of the Warriors, the Prisoners, and the Booty. - Moses commanded the men of war to remain for seven days outside the camp of the congregation, to carry out upon the third and seventh day the legal purification of such persons and things as had been rendered unclean through contact with dead bodies. Every one who had slain a soul (person), or touched one who had been slain, was to be purified, whether he were a warrior or a prisoner. And so also were all the clothes, articles of leather, materials of goats' hair, and all wooden things. Numbers 31:21”