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."
Cross References (ranked by relevance)
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 defiled by the dead:
1 Chronicles 22:8
But the word of the LORD came to me, saying, Thou hast shed blood abundantly, and hast made great wars: thou shalt not build an house unto my name, because thou hast shed much blood upon the earth in my sight.