וְאַתֶּ֗ם חֲנ֛וּ מִח֥וּץ לַֽמַּחֲנֶ֖ה שִׁבְעַ֣ת יָמִ֑ים כֹּל֩ הֹרֵ֨ג נֶ֜פֶשׁ וְכֹ֣ל ׀ נֹגֵ֣עַ בֶּֽחָלָ֗ל תִּֽתְחַטְּא֞וּ בַּיּ֤וֹם הַשְּׁלִישִׁי֙ וּבַיּ֣וֹם הַשְּׁבִיעִ֔י אַתֶּ֖ם וּשְׁבִיכֶֽם׃
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.
Read kabbalistic (mystical) interpretation of Numbers 31:19: and classical mystical sources.