Genesis 30:4-8

So Rachel gave Bilhah, her slave girl, to Jacob as a wife, and he had sexual relations with her. She became pregnant and gave Jacob a son. Rachel said, “God has judged me innocent. He has listened to my prayer and has given me a son,” so she named him Dan. Bilhah became pregnant again and gave Jacob a second son. Rachel said, “I have struggled hard with my sister, and I have won.” So she named that son Naphtali.