Abraham 2

 Though I have read many reasons of why Abraham was justified in telling Pharoah that Sarai was his sister, the one the justifies all is - 

"...the Lord said unto me: Behold, Sarai, thy wife, is a very fair woman to look upon;

23 Therefore it shall come to pass, when the Egyptians shall see her, they will say—She is his wife; and they will kill you, but they will save her alive; therefore see that ye do on this wise:

24 Let her say unto the Egyptians, she is thy sister, and thy soul shall live."  (Abraham 2:22–24)

Receiving this instruction from the Lord justifies all actions.