Genesis 30:4-8

So she gave him Bilhah her maid as a [secondary] wife, and Jacob went in to her. Bilhah conceived and gave birth to a son for Jacob. Then Rachel said, “God has judged and vindicated me, and has heard my plea and has given me a son [through my maid].” So she named him Dan (He judged). Bilhah, Rachel’s maid, conceived again and gave birth to a second son for Jacob. So Rachel said, “With mighty wrestlings [in prayer to God] I have struggled with my sister and have prevailed.” So she named him Naphtali (my wrestlings).