וַיֶּעְתַּ֨ר יִצְחָ֤ק לַֽיהוָה֙ לְנֹ֣כַח אִשְׁתּ֔וֹ כִּ֥י עֲקָרָ֖ה הִ֑וא וַיֵּעָ֤תֶר לוֹ֙ יְהוָ֔ה וַתַּ֖הַר רִבְקָ֥ה אִשְׁתּֽוֹ׃
And Isaac entreated the LORD for his wife, because she was barren; and the LORD let Himself be entreated of him, and Rebekah his wife conceived.
Rashi on Genesis
וַיֶּעְתַּר AND ISAAC ENTREATED —He prayed much and urgently.
Rashbam on Genesis
ויעתר, an expression denoting a lengthy prayer, as in Ezekiel 35,13 העתרתם עלי דבריכם, “you multiplied your words against Me.”
Sforno on Genesis
לנכח אשתו, even though he had been given an assurance from G’d that he would produce seed, he prayed to G’d that the mother of this child or children should be someone who was meritorious, someone of the calibre of Rivkah who was present and standing opposite him..