Genesis 38:11-15

Then Judah said to his daughter-in-law Tamar, “Remain a widow in your father’s house until my son Shelah grows up”; for he thought, “I am afraid that he too may die like his brothers.” So Tamar went and lived in her father’s house.

Now after a considerable time Shua’s daughter, the wife of Judah, died; and when the time of mourning was ended, Judah went up to his sheepshearers at Timnah, he and his friend Hirah the Adullamite.

And Tamar was told, “Behold, your father-in-law is going up to Timnah to shear his sheep.”

So she removed her widow’s garments and covered herself with a veil, and wrapped herself, and sat in the gateway of Enaim, which is on the road to Timnah; for she saw that Shelah had grown up, and she had not been given to him as a wife.

When Judah saw her, he assumed she was a prostitute, for she had covered her face.