Genesis 30:3-7

Then she said, “Here is my female slave Bilhah: have relations with her that she may give birth on my knees, so that by her I too may obtain a child.”

So she gave him her slave Bilhah as a wife, and Jacob had relations with her.

Bilhah conceived and bore Jacob a son.

Then Rachel said, “God has vindicated me, and has indeed heard my voice and has given me a son.” Therefore she named him Dan.

And Rachel’s slave Bilhah conceived again and bore Jacob a second son.