Midrash sa Genesis 17:18: Bereshit Rabbah & Aggadat Bereshit

“Abraham said to God: Would that Ishmael might live before You” (Genesis 17:18).
“God said: But Sarah your wife will bear you a son, and you shall call his name Isaac, and I will keep My covenant with him for an eternal covenant, for his descendants after him” (Genesis 17:19).
“Would that Ishmael might live before You” – Rabbi Yudan said in the name of Rabbi Yehuda bar Simon: This is analogous to a friend of the king, to whom he would provide a stipend. The king said to him: ‘I wish to double your stipend.’ He said to him: ‘Do not seek to provide me such great satisfaction; would that you not revoke the previous one.’ So, [Abraham said:] “Would that Ishmael might live before You.” “God said: But Sarah your wife.”

Chapter (72) 73: Torah [1] "And the El Shaddai grant you mercy" (Genesis 43:14). As it is written in scriptures: Knowledge [of escape from You] is concealed from me. It is too formidable. I cannot know it. (Psalm 139:6). What is the meaning of "extraordinary level of understanding beyond my grasp"? It refers to something that is difficult for a person to comprehend, as it says, "If there arise among you a matter too hard for judgment" (Deuteronomy 17:8). Jacob said, "I cannot understand this matter." God promised Abraham that he would have twelve tribes, as it says, "Look now toward heaven, and tell the stars, if thou be able to number them...So shall thy seed be" (Genesis 15:5). Just as there are twelve constellations in the heavens that govern the world, so too I will establish twelve tribes from you that will govern the world, as it is said, "Thus shall your seed be" (Genesis 15:5). When Ishmael was born and he begot twelve princes, as it is said, "And he shall be a wild ass of a man: his hand shall be against every man, and every man's hand against him; and he shall dwell in the face of all his brethren" (Genesis 16:12), Abraham thought that these were the twelve tribes. But God said to him, "No, not those that you think. Sarah will bear a son for you" (Genesis 17:19), as it is said, "And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac" (Genesis 21:12). It is through Isaac that your seed will be called (Genesis 21:12), as I said to you, "Thus shall your seed be" (Genesis 15:5). When Isaac married Rebecca and she was found to be barren, he began to question how the promise that God made to Abraham could be fulfilled, as she was barren, as it is said, "And Isaac entreated the Lord for his wife, because she was barren" (Genesis 25:21), and the children struggled within her (Genesis 25:22). "I'm sorry," she began, "if that's the case, I apologize to one another and "She went to inquire of יהוה," (Genesis 25:22), went to the study hall of Shem, and the Lord said to her, 'Two nations are in your womb, and two peoples shall be separated from your body' (Genesis 25:23). Why did she say why is it? (Genesis 25:22), "this" is numerically equivalent to 12. And God said to her [Sarah], "What you think is not so, but there are two nations in your womb." When Jacob stood up and went out to Laban, Isaac called him and said to him, "Let it be known that the Lord is establishing twelve tribes from you," as it is said, "Isaac called Jacob and blessed him, and commanded him, and said to him, 'Do not marry a Canaanite woman. Arise, go to Padan Aram, to the house of Bethuel, your mother's father, and take a wife from there of the daughters of Laban, your mother's brother. And may God Almighty bless you, and make you fruitful, and multiply you, that you may be a congregation of peoples; and give you the blessing of Abraham, to you and your descendants with you" (Genesis 28:1-4). The blessing that He blessed Abraham with, saying, "Look up now" (Genesis 15:5), is fulfilled through you. And once Jacob went and took wives and fathered twelve tribes, as it says, "And the sons of Jacob were twelve" (Genesis 35:22), Joseph began to see hints of it in his dream, saying, "Behold, I have dreamed a dream" (Genesis 37:9). Jacob began to keep watch over his father's words, and his father kept the matter (Genesis 37:11). And when Joseph was sold and Simeon was bound and Benjamin was brought to take revenge, Jacob began to cry out, "Me? What do I know? I thought that from my fathers I would establish twelve tribes, but I am dwindling and going down," as it says, "Joseph is gone" (Genesis 42:36). Everything that the old man promised was fulfilled, and yet I am decreasing and going down. "How incomprehensible is this to me," as it says, "I do not know what to say to you, but one thing remains in my hand, the blessing that my father blessed me with, saying, 'And Almighty God bless you'" (Genesis 28:3).