the sons of Leah were Reuben, Jacob's firstborn, and Simeon, Levi, Judah, Issachar, and Zebulun;
Genesis 35:23
Surrounding context
35:22 And it happened, when Israel dwelt in that land, that Reuben went and lay with Bilhah his father's concubine; and Israel heard about it. Now the sons of Jacob were twelve:
35:23 the sons of Leah were Reuben, Jacob's firstborn, and Simeon, Levi, Judah, Issachar, and Zebulun;
35:24 the sons of Rachel were Joseph and Benjamin;