Leviticus 15:24
And if any man lie with her at all, and her flowers be upon him, he shall be unclean seven days; and all the bed whereon he lieth shall be unclean.
Cross-reference
Leviticus 15:33
Parallel
Leviticus 15:33 summarizes the laws for discharges, including the case of lying with a menstruating woman — the same situation as here.
Leviticus 20:18
Contrast
Leviticus 20:18 imposes a severe penalty (cut off) for the same act — contrasting the impurity penalty here with a moral/penal consequence.
Leviticus 18:19
Parallel
Leviticus 18:19 repeats the same prohibition in the sexual relations list — a direct parallel restating the rule.