Genesis 30:9-12
9 When Leah saw that she had stopped having children, she took her maidservant Zilpah and gave her to Jacob as a wife.
10 Leah’s servant Zilpah bore Jacob a son.
11 Then Leah said, “What good fortune!” So she named him Gad.
12 Leah’s servant Zilpah bore Jacob a second son.