Charles Ellicott Commentary Genesis 20:13

"and it came to pass, when God caused me to wander from my father`s house, that I said unto her, This is thy kindness which thou shalt show unto me. At every place whither we shall come, say of me, He is my brother." — Genesis 20:13 (ASV)

When God caused me to wander. — According to rule, Elohim is construed with a verb singular for the true God, but with a verb plural for false gods. Here the verb is plural, and the same construction occurs in Genesis 35:7; Exodus 22:9; 2 Samuel 7:22 (but singular in 1 Chronicles 17:20); and Psalm 58:11. Moreover, in Joshua 24:19, Elohim is joined with an adjective (holy) in the plural. These exceptions may either be relics of a less strict use of the name Elohim or errors of copyists, misled by the ordinary rules of grammar. This latter view is confirmed by the fact that the Samaritan Pentateuch, both here and in Genesis 35:7, has the singular.

At every place. — The fact that this compact between Abraham and Sarah had been made so long before, would convince Abimelech that their conduct was not occasioned by anything they had seen at Gerar .