VOD, Genesis 20:2

And here is one of the moments where Abraham failed a test of faith...instead of trusting God and believing that He was in control, Abraham let his fear take over and dictate his actions (though Sarah actually was his half-sister, he should've said she is my wife).

Now Abraham said of Sarah his wife, "She is my sister." And Abimelech, king of Gerar, sent and took Sarah. Genesis 20:2 (NKJ)