Numbers 31:24

And ye shall wash your clothes on the seventh day, and ye shall be clean, and afterward ye shall come into the camp.

Cross-reference

Numbers 19:19 prescribes the same seventh-day washing after impurity — reinforcing this specific purification ritual.

Leviticus 14:9 commands washing clothes on the seventh day for leper cleansing — identical timing and action.

Leviticus 15:13 requires washing clothes on the seventh day after a discharge — the same purification pattern.

Exodus 19:10 commands washing garments for consecration before meeting God — a parallel purification practice.