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If you are asking what John said to Dean right before he died, he told Dran that Sam might turn evil because of what the Yellow Eyed Demon dod to Sam as an infant. He said if you can't save him, you'll have to kill him. 

John Winchester Dies To Save Dean\n\n Dean and Sam eventually avenge their parents, killing Azazel in the season 2 finale, "All Hell Breaks Loose, Part 2." Dean even gets an assist from John, who emerges from Hell, where time passes differently, as a ghost, fights Azazel and then ascends to Heaven in peace.