Leviticus 14:9

But it shall be on the seventh day, that he shall shave all his hair off his head and his beard and his eyebrows, even all his hair he shall shave off: and he shall wash his clothes, also he shall wash his flesh in water, and he shall be clean.

Cross-reference

Numbers 8:7 requires Levites to shave all body hair, wash clothes, and cleanse with water, a near identical purification ritual.

Numbers 19:19 prescribes washing clothes and bathing on the seventh day for purification after contact with a dead body, closely paralleling this.

Numbers 6:9 also has the Nazirite shaving his head on the seventh day for purification after defilement, echoing this same timing.

Hebrews 9:10 summarizes OT regulations about washings and external cleansings, showing they were temporary until Christ.