Genesis 30:4-8

So Rachel gave her servant Bilhah to Jacob as another wife, and Jacob slept with her. And Bilhah conceived and bore Jacob a son, and Rachel named him Dan, saying, “God has vindicated me. He heard my voice and gave me a son.” Then her servant Bilhah conceived again and bore Jacob a second son. Rachel named him Naphtali, saying, “I have wrestled mightily with my sister, and I won!”