"And the LORD had blessed Abraham in all things" (Genesis 24:1). Already while he was between the pieces [at the Covenant of the Pieces], He brought him the good tidings that He would give him a son after fifty-two years. At the age of forty-eight he recognized his Creator, and at that very moment He announced the tidings to him. "In all things" - by the merit of the tithe, as it is said, "and he gave him a tithe of all" (Genesis 14:20).
Abraham Blessed in All by the Merit of the Tithe
Yalkut Shimoni on Torah 106:1
וַה' בֵּרַךְ אֶת אַבְרָהָם בַּכֹּל, עַד שֶׁהוּא בֵּין הַבְּתָרִים בִּשְּׂרוֹ שֶׁהוּא נוֹתֵן לוֹ בֵּן אַחַר חֲמִשִּׁים וּשְׁתַּיִם שָׁנָה בֶּן אַרְבָּעִים וּשְׁמוֹנֶה שָׁנָה הִכִּיר לְבוֹרְאוֹ, בְּאוֹתָה שָׁעָה בִּשְּׂרוּ. בַּכֹּל, בִּזְכוּת הַמַּעֲשֵׂר שֶׁנֶּאֱמַר (בראשית יד, כ) "וַיִּתֵּן לוֹ מַעֲשֵׂר מִכֹּל".