Midrash sur La Genèse 24:67

“The sun rises and the sun sets, and it hastens to its place where it arises” (Ecclesiastes 1:5).
“The sun rises.” Rabbi Berekhya said in the name of Rabbi Abba bar Kahana: Don’t we know that “the sun rises and the sun sets”? Rather, to what is it [alluding]? Before the sun of one righteous individual sets, He causes the sun of another righteous individual to rise. The day that Rabbi Akiva died, Rabbi [Yehuda HaNasi] was born, and they read this verse in his regard: “The sun rises and the sun sets.” The day that Rav Ada bar Ahava died, Rav Hamnuna his son was born, and they read in his regard: “The sun rises and the sun sets.” The day that Rav Hamnuna died, Rabbi Avin his son was born, and they read in his regard: “The sun rises and the sun sets.” The day that Rabbi Avin died, Abba Hoshaya of Teraya was born, and they read in his regard: “The sun rises and the sun sets.” Before the sun of Sarah set, the sun of Rebecca rose. That is what is written: “Betuel begot Rebecca” (Genesis 22:23), and then, “Sarah died in Kiryat Arba” (Genesis 23:2), and it is written: “Isaac brought her into the tent of his mother Sarah” (Genesis 24:67).³⁰See Bereshit Rabba 60:16, where this verse is interpreted to mean that Rebecca was a worthy replacement for Sarah. Before the sun of Moses set, the sun of Joshua rose. Before the sun of Joshua set, the sun of Otniel, who is Yabetz, rose. So it is with all of them in each and every generation; that is, “the sun rises and the sun sets.”

And Abraham took another wife (Gen. 25:1). What is written previously concerning this matter? And Isaac brought her into his mother Sarah’s tent (Gen. 24:67). You learn from this that if a man’s wife should die, leaving him sons, he should not remarry until his sons are betrothed. Only then should he remarry. Abraham did so. After Sarah’s death, he first betrothed Isaac and then took a wife for himself. Where do we learn this? It is written: Isaac brought her into his mother Sarah’s tent, and after: Abraham took another wife. Isaac said to himself: “I have taken a wife, but my father is without a wife.” What did Isaac do? He went and bought him (Abraham) a wife. Rabbi said: Hagar and Keturah were one and the same person. Why then was she called Keturah? Because she had been bound up (keshurah) like a water bag.⁸Indicating that she was a virgin.

Rabbi Simeon said: Abraham spake to Isaac his son (saying), This servant is suspected of all the transgressions of the Torah, and deceit is in this servant, as it is said, "He is a Canaanite, the balances of deceit are in his hand; he loveth to defraud" (Hos. 12:7). See, lest he has defiled her, therefore bring the girl into the tent and examine her tactually; || and if she be undefiled, behold, she is destined for thee from her mother's womb. He brought her into the tent and examined her tactually, and he showed the result to Abraham his father, and afterwards he took her to be his wife, as it is said, "And Isaac brought her into the tent of Sarah his mother… And Isaac was comforted after his mother's death" (Gen. 24:67); for the deeds of Rebecca were like unto those of Sarah. Hence the Israelites have the custom of producing the tokens of the damsel's virginity, as it is said, "Then shall the father of the damsel, and her mother, take and bring forth the tokens of the damsel's virginity" (Deut. 22:15).