וְאִ֕ישׁ כִּֽי־תֵצֵ֥א מִמֶּ֖נּוּ שִׁכְבַת־זָ֑רַע וְרָחַ֥ץ בַּמַּ֛יִם אֶת־כָּל־בְּשָׂר֖וֹ וְטָמֵ֥א עַד־הָעָֽרֶב׃
And if the flow of seed go out from a man, then he shall bathe all his flesh in water, and be unclean until the even.
Read kabbalistic (mystical) interpretation of Leviticus 15:16: and classical mystical sources.