"And it came to pass after these things that it was told to Abraham, saying, Behold, Milcah also has borne children" (Genesis 22:20). It is written, "A sound heart is the life of the flesh" (Proverbs 14:30). For while he was still on Mount Moriah, he received the good news that his son's mate had been born, as it is said, "And Bethuel begot Rebecca."
News of Rebecca's Birth Reaches Abraham on the Mountain
Yalkut Shimoni on Torah 102:3
(בראשית כב כ-כד) וַיְּהִי אַחֲרֵי הַדְּבָרִים הָאֵלֶה וַיֻּגַּד לְאַבְרָהָם לֵאמֹר הִנֵּה יָלְדָה מִלְכָּה, כְּתִיב, (משלי יד, ל) "חַיֵּי בְשָׂרִים לֵב מַרְפֵּא" שֶׁעַד שֶׁהוּא בְּהַר הַמּוֹרִיָּה נִתְבַּשֵּׂר שֶׁנּוֹלְדָה בַּת זוּגוֹ, שֶׁנֶּאֱמַר, וּבְתוּאֵל יָלַד אֶת רִבְקָה.