Beraishis 15C – Avraham calls God by the name אֲ-דֹ-נָ-י יֱ-ה-וִ-ה

וַיֹּאמֶר אַבְרָם אֲדֹנָי יֱהוִה מַה תִּתֶּן לִי וְאָנֹכִי הוֹלֵךְ עֲרִירִי וּבֶן מֶשֶׁק בֵּיתִי הוּא דַּמֶּשֶׂק אֱלִיעֶזֶר

This is the first time in Scripture that this designation of God is used. It only appears 3 other times. (See commentary)

Avraham was the first person to call God “אדון”. This is a name that is always mentioned by an עבד השם, a prophet. A person who serves God and who is like an instrument in God’s hand calls God “אדון”. He uses the plural from (not Adoni) to proclaim that there are no other masters. God is not a master among other masters. God is “all the masters”; the Only Master.

יֱהוִה is a combination of two Names. It is written in the form of the attribute of mercy and is pronounced in the form of the attribute of strict justice. This signifies that even when God acts through His attribute of strict justice, mercy in inherent in the justice. Even when God conducts Himself in His attribute of justice, He lays the foundation for a blessed future. It is the same God of mercy, only it is prounounced (GS-perceived) as the God of strict justice.

Beraishis 15:2
pages 350-351