(19) This is the story of Isaac, son of Abraham. Abraham begot Isaac. (20) Isaac was forty years old when he took to wife Rebekah, daughter of Bethuel the Aramean of Paddan-aram, sister of Laban the Aramean. (21) Isaac pleaded with the LORD on behalf of his wife, because she was barren; and the LORD responded to his plea, and his wife Rebekah conceived.
א"ר יצחק מפני מה היו אבותינו עקורים מפני שהקב"ה מתאוה לתפלתן של צדיקים א"ר יצחק למה נמשלה תפלתן של צדיקים כעתר מה עתר זה מהפך התבואה ממקום למקום כך תפלתן של צדיקים מהפכת מדותיו של הקב"ה ממדת רגזנות למדת רחמנות
Rabbi Yitzḥak said: For what reason were our forefathers initially infertile? Because the Holy One, Blessed be He, desires the prayers of the righteous, and He therefore wanted them to pray for children. Similarly, Rabbi Yitzḥak said: Why are the prayers of the righteous compared to a pitchfork [eter], as in the verse: “And He let Himself be entreated [vaye’ater]”? This indicates that just as this pitchfork turns over produce from one place to another, so the prayer of the righteous turns over the attributes of the Holy One, Blessed be He, from the attribute of rage to the attribute of mercy.
(יא) רבי יהודה אומר, עשרים שנה היתה רבקה עקרה, לאחר עשרים שנה לקחה יצחק והלך עמה להר המוריה למקום שנעקד שם, והתפלל על ההריון ונעתר לו, שנאמ׳ ויעתר לו ה׳ וגו׳.
(11) Rabbi Jehudah said: Rebecca was barren for twenty years. After twenty years (Isaac) took Rebecca and went (with her) to Mount Moriah, to the place where he had been bound, and he prayed on her behalf concerning the conception of the womb; and the Holy One, blessed be He, was entreated of him, as it is said, "And Isaac intreated the Lord" (ibid. xxv. 21).
(ה) וַיֶּעְתַּר יִצְחָק לַה' לְנֹכַח אִשְׁתּוֹ (בראשית כה, כא), רַבִּי יוֹחָנָן וְרֵישׁ לָקִישׁ, רַבִּי יוֹחָנָן אָמַר שֶׁשָּׁפַךְ תְּפִלּוֹת בְּעשֶׁר. רֵישׁ לָקִישׁ אָמַר שֶׁהִפֵּךְ אֶת הַגְּזֵרָה, וּלְפוּם כֵּן קָרְיִן לֵיהּ עַתְרָא דְּאַפֵּךְ אִדְּרָא. לְנֹכַח אִשְׁתּוֹ, מְלַמֵּד שֶׁהָיָה יִצְחָק שָׁטוּחַ כָּאן, וְהִיא שְׁטוּחָה כָּאן, וְאוֹמֵר רִבּוֹנוֹ שֶׁל עוֹלָם כָּל בָּנִים שֶׁאַתָּה נוֹתֵן לִי יִהְיוּ מִן הַצַּדֶּקֶת הַזּוֹ, אַף הִיא אָמְרָה כֵּן, כָּל בָּנִים שֶׁאַתְּ עָתִיד לִתֵּן לִי יִהְיוּ מִן הַצַּדִּיק הַזֶּה.
(5) "Isaac pleaded with the LORD on behalf of his wife" (Genesis 25, 21), Rebi Yochanan and Reish Lakish- Rebi Yochanan says that (the word 'plead' means) he poured forth a wealth of prayers. Reish Lakish says it means that his prayers overturned God's decree, and therefore a windowing shovel is referred to as an עתרא, for it overturns the grain in the threshing place.
"on behalf of his wife" This teaches that Isaac was prostrated in prayer here and [Rebecca] was prostrated in prayer there. And Isaac said in his supplication: "Master of the universe! [May] all the children that You will give to me be from this righteous woman." [Rebecca] too said thus: "May all of the children that You will give to me in the future be from this righteous man."