Numbers 31:19

And encamp ye without the camp seven days: whosoever hath killed any person, and whosoever hath touched any slain, purify yourselves on the third day and on the seventh day, ye and your captives.

Numbers 5:2

Command the children of Israel, that they put out of the camp every leper, and every one that hath an issue, and whosoever is unclean by the dead:

Numbers 19:11-22

He that toucheth the dead body of any man shall be unclean seven days:

But the word of Jehovah came to me, saying, Thou hast shed blood abundantly, and hast made great wars: thou shalt not build a house unto my name, because thou hast shed much blood upon the earth in my sight.

Treasury of Scripture Knowledge

Summary

Numbers 31:19

And do ye abide without the camp seven days: whosoever hath killed any person, and whosoever hath touched any slain, purify both yourselves and your captives on the third day, and on the seventh day.