Jamieson, Fausset and Brown on Genesis 20:12

12. yet indeed she is my sister--(See on Ge 11:31). What a poor defense Abraham made. The statement absolved him from the charge of direct and absolute falsehood, but he had told a moral untruth because there was an intention to deceive (compare Ge 12:11-13). "Honesty is always the best policy." Abraham's life would have been as well protected without the fraud as with it: and what shame to himself, what distrust to God, what dishonor to religion might have been prevented! "Let us speak truth every man to his neighbor" [Zec 8:16; Ep 4:25].