Genesis 30:9-13
When Leah saw that she had left bearing, she took Zilpah her maid, and gave her Jacob to wife.
Nave's Topical Index—AKJV

Genesis 35:26
And the sons of Zilpah, Leah's handmaid: Gad, and Asher: these are the sons of Jacob, which were born to him in Padanaram.
Nave's Topical Index—AKJV

Genesis 37:2
These are the generations of Jacob. Joseph, being seventeen years old, was feeding the flock with his brothers; and the lad was with the sons of Bilhah, and with the sons of Zilpah, his father's wives: and Joseph brought to his father their evil report.
Nave's Topical Index—AKJV

Genesis 46:18
These are the sons of Zilpah, whom Laban gave to Leah his daughter, and these she bore to Jacob, even sixteen souls.
Nave's Topical Index—AKJV