Exodus 3:6

וַיֹּאמֶר אָנֹכִי אֱלֹקי אָבִיךָ אֱלֹקי אַבְרָהָם אֱלֹקי יִצְחָק וֵאלֹקי יַעֲקֹב וַיַּסְתֵּר מֹשֶׁה פָּנָיו כִּי יָרֵא מֵהַבִּיט אֶל הָאֱלֹקים

He said, "I am the G-d of your father, the G-d of Abraham, the G-d of Isaac and the G-d of Jacob." Moses hid his face because he was afraid to gaze upon G-d.

In Shemoneh Esrei, we refer to Hashem as “G-d of our fathers, the G-d of Abraham, the G-d of Isaac and the G-d of Jacob.” The reason we do this is because it’s how G-d referred to Himself when speaking to Moshe. But the verse says that Hashem is the G-d of our “father” in the singular! The Ramban explains that this is the same as “G-d of your fathers,” since each one of the Patriarchs is individually called a father. He points out similar usage of the singular in Exodus 15:2, “this is my G-d and I will glorify Him; my father’s G-d, and I will exalt Him.”