Genesis 30:4 (BSB)

So Rachel gave Jacob her servant Bilhah as a wife, and he slept with her,

From Genesis 30. Also in the ESV.

Commentary on Genesis 30:4

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Genesis 30:1-13: We have here the bad consequences of that strange marriage which Jacob made with the two sisters. Here is, I. An unhappy disagreement between him and Rachel (Gen 30:1, Gen 30:2), occasioned, not so much by her own barrenness as by her sister's fruitfulness.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Genesis 30:4: And she gave him Bilhah her handmaid,.... To be enjoyed as a wife, though she was no other than a concubine; yet such were sometimes called wives, and were secondary ones, and were under the proper lawful wife, nor did their children inherit; but those which Jacob had by his wives' maids did inherit with the rest: and Jacob went in unto her; consenting to...
• Keil & Delitzsch (Lutheran), Biblical Commentary on the Old Testament on Genesis 30:1-8: Gen 30:1-8 Bilhah’s Sons. - When Rachel thought of her own barrenness, she became more and more envious of her sister, who was blessed with sons. But instead of praying, either directly or through her husband, as Rebekah had done, to Jehovah, who had promised His favour to Jacob (Gen 28:13.), she said to Jacob, in passionate displeasure, “Get me children, or I shall die;”...