Midrash su Rut 4:17

The disciples of R. Jose questioned him: "How did David marry two sisters while they were both living?" He answered them: "He married Michal after the death of Merab." And R. Jose said so in accordance with his own theory, for we are taught in a Baraitha: R. Jose used to lecture about the following two confused passages: It is written (II Sam. 21, 8) And the king took the two sons of Rizpah, the daughters of Ayah, whom she had born unto Saul, Armoni and Mephibosheth; and the five sons of Michal, the daughler of Saul, whom she had borne to Adriel, the son of Barzillai the Mehollathite. But was Michal given to Adriel? Was she not given to Palti b. Layish? as it is written (Ib. 25, 44) But Saul had given Michal his daughter, David's wife, to Palti, the son of Layish. Hence the Scriptures equalize the betrothing of Merab to Adriel to the betrothing of Michal to Palti b. Layish. Just as the betrothing of Michal to Palti was a sin because she was already the wife of David, so also was the betrothing of Herab to Adriel a sin because she was already David's wife. But what would R. Joshua b. Karcha say to the passage which reads: The five sons of Michal, the daughter of Saul? Did then, Michal hear them? Was it not Merab who bore them? R. Joshua will answer that Merab bore them and Michal merely brought them up, and therefore they bore the name of Michal. This is to teach you that the one who brings up an orphan is considered by Scriptures as if he bore the child. R. Chanina says: "This is inferred from (Ruth 4, 17) There hath been a son born unto Naomi, etc. Did, then, Naomi bear him? Was it not, in fact, Ruth who bore him? Therefore we must say that, though Ruth bore him, he was nevertheless brought up by Naomi, and therefore is he called after her." R. Jochanan said: "From the following (I Chr. 4, 18) And his wife the Jewess bore Jered the father of Gedor, and Heber the father, etc., and these are the sons of Bithiah, the daughter of Pharaoh, whom Mered had taken [for wife]. Mered refers to Caleb, and why was he called Mered (rebel)? Because he rebelled against the accusation of the spies. And was he then born of Bithiah? Behold he was born of Jochcbed? We must therefore say that, though he was born of Jochebed, he was nevertheless raised by Bithiah, and therefore he is called after her name." R. Eliezer said: From the following (Ps. 77, 16) Thou hast with Thine arm redeemed Thy people, the sons of Jacob and Joseph. Selah, Were they, then, born to Joseph, and not to Jacob? They were born to Jacob, but Joseph fed them, and therefore they were named after him.