וְהַשֹּׂרֵ֣ף אֹתָ֔הּ יְכַבֵּ֤ס בְּגָדָיו֙ בַּמַּ֔יִם וְרָחַ֥ץ בְּשָׂר֖וֹ בַּמָּ֑יִם וְטָמֵ֖א עַד־הָעָֽרֶב׃
And he that burneth her shall wash his clothes in water, and bathe his flesh in water, and shall be unclean until the even.
Read kabbalistic (mystical) interpretation of Numbers 19:8: and classical mystical sources.