Rabbi Yitzchak said: Isaac our father was sterile, as it is said, "And Isaac entreated the LORD opposite his wife" (Genesis 25:21). It does not say "on behalf of his wife" but "opposite his wife," teaching that both of them were barren. If so, why does it say "and the LORD was entreated of him" rather than "the LORD was entreated of them"? Because the prayer of a righteous one who is the son of a righteous one is not comparable to the prayer of a righteous one who is the son of a wicked one. Rabbi Yitzchak said: Why were our patriarchs barren? Because the Holy One, blessed be He, longs for the prayer of the righteous. Why is their prayer likened to a pitchfork? As above. Rabbi Yehudah says: For twenty years Rebecca was barren. After twenty years he took Rebecca and went to Mount Moriah, to the place where he had been bound, and prayed there over the conception of the womb, and the Holy One, blessed be He, was entreated of him, as it is said, "and the LORD was entreated of him" (Genesis 25:21).
Isaac and Rebecca Both Barren and the Entreaty God Desired
Yalkut Shimoni on Torah 110:16
אָמַר רַבִּי יִצְחָק, יִצְחָק אָבִינוּ עָקָר הָיָה, שֶׁנֶּאֱמַר וַיֶּעְתַּר יִצְחָק לַה' לְנֹכַח אִשְׁתּוֹ, עַל אִשְׁתּוֹ לֹא נֶאֱמַר אֶלָּא לְנֹכַח אִשְׁתּוֹ, שֶׁשְׁנֵיהֶם עֲקוּרִים הָיוּ. אִי הֲכִי וַיֵּעָתֶר לוֹ ה' וַיֵּעָתֶר לָהֶם מִבַּעְיָא לֵיהּ אֶלָּא לְפִי שֶׁאֵינוֹ דּוֹמָה תְּפִלַּת צַדִּיק בֶּן צַדִּיק לִתְפִלַּת צַדִּיק בֶּן רָשָׁע. אָמַר רַבִּי יִצְחָק, מִפְּנֵי מָה הָיוּ אֲבוֹתֵינוּ עֲקוּרִים, מִפְּנֵי שֶׁהַקָּדוֹשׁ בָּרוּךְ הוּא מִתְאַוֶּה לִתְפִלָּתָן שֶׁל צַדִּיקִים. לָמָּה נִמְשְׁלָה תְּפִלָּתָן לְעֶתֶר וְכוּ' כְּדְלְעֵיל. רַבִּי יְהוּדָה אוֹמֵר, עֶשְׂרִים שָׁנָה הָיְתָה רִבְקָה עֲקָרָה, וּלְאַחַר עֶשְׂרִים שָׁנָה לָקַח אֶת רִבְקָה וְהָלַךְ לוֹ לְהַר הַמּוֹרִיָּה, לַמָּקוֹם שֶׁנֶּעֱקַד שָׁם, וְנִתְפַּלֵּל עָלֶיהָ עַל הֵרָיוֹן הַבֶּטֶן, וְנֶעְתַּר לוֹ הַקָּדוֹשׁ בָּרוּךְ הוּא, שֶׁנֶּאֱמַר וַיֵּעָתֶר לוֹ.