Bilhah (Hebrew: בִּלְהָה, Bilhāh; "faltering, bashful") was the handmaid of Laban and given to his daughter Rachel after Rachel became Jacob's wife. (Genesis 29:29) When Rachel had trouble conceiving, she had Jacob sleep with Bilhah to have children through her, as was the custom in the ancient mideast at that time. Bilhah had two offspring through Jacob, Dan and Naphtali his fifth and sixth sons respectively. (Genesis 30:3 - 30:8)
“God has vindicated me, and has indeed heard my voice and has given me a son.”
Reuben later had an illicit affair with Bilhah, and that indiscretion cost Reuben his birthright.