Charles Ellicott Commentary 1 Chronicles 2:4

"And Tamar his daughter-in-law bare him Perez and Zerah. All the sons of Judah were five." — 1 Chronicles 2:4 (ASV)

Tamar. —Wife of Er. The story of her incest with Judah, the fruit of which was the twins Pharez (Hebrew, Perez) and Zerah (called Zarah, Genesis 38:30; and Zara, Matthew 1:3), is told in Genesis 38:8-30.