Genesis 30:3

על ברכי UPON MY KNEES — as the Targum takes it: she will bear children and I will rear them. ואבנה גם אנכי AND I ALSO MAY HAVE CHILDREN — What force has “also”? She said to him, “Your grandfather, Abraham, had children from Hagar and yet he girded up his loins (actively interceded) for Sarah and she afterwards was blessed with a child”. He replied, “But my grandmother brought an associate wife unto her house”. She retorted, “If that is what prevents me being blessed with children, הנה אמתי BEHOLD MY HANDMAID” etc. ואבנה נם אנכי AND I ALSO MAY HAVE CHILDREN through her as Sarah was built up through her handmaid (Genesis Rabbah 71:7).

And she said, Behold my maid Bilha, go in to her; and she shall bear upon my knees, that I may also have children by her.

וַתֹּ֕אמֶר הִנֵּ֛ה אֲמָתִ֥י בִלְהָ֖ה בֹּ֣א אֵלֶ֑יהָ וְתֵלֵד֙ עַל־בִּרְכַּ֔י וְאִבָּנֶ֥ה גַם־אָנֹכִ֖י מִמֶּֽנָּה׃