Genesis 31:35

And she said to her father, Let it not displease my lord that I cannot rise up before thee, as filial respect would have demanded; for the custom of women is upon me. Whether this was actually true or not, she proved herself a worthy daughter of a cunning father, for the ruse served to keep Laban from looking under the saddle which Rachel was using as a couch. At a later period this matter was regulated by law, Leviticus 15:19 ff. Thus the Lord did not permit Jacob, who knew nothing of Rachel's trick, to be put to shame.