Genesis 38:26-30

Judah recognized them and said, “She is more in the right than I. She did this because I did not give her to my son Shelah as I promised.” And Judah did not have sexual relations with her again. When the time came for Tamar to give birth, there were twins in her body. While she was giving birth, one baby put his hand out. The nurse tied a red string on his hand and said, “This baby came out first.” But he pulled his hand back in, so the other baby was born first. The nurse said, “So you are able to break out first,” and they named him Perez. After this, the baby with the red string on his hand was born, and they named him Zerah.