“…and it came about, when God caused me to wander from my father’s house, that I said to her, ‘This is the kindness which you will show to me: everywhere we go, say of me, “He is my brother.”’ Gen. 20:13

The word used for God here is the plural “Elohim“, which could be translated as gods.  This may actually be referring to Abraham leaving his father Terah (see Genesis 12:1-5) due to him being an idolator in we see in Joshua 24:2:

“Joshua said to all the people, “This is what the LORD, the God of Israel, says: ‘Long ago your forefathers, including Terah the father of Abraham and Nahor, lived beyond the River and worshiped other gods.'””

Friedman notes that Abraham speaks in this manner because he is addressing a pagan king, and that Abimelech has not yet told Abraham that he had an encounter with the one true God.

We may be tempted to state that this is a reference to the Triune Godhead, comprised of God the Father, the Lord Jesus Christ, and the Holy Spirit, which is also a possibility, however the context would not seem to have the same significance as the other interpretations.