1 Samuel 15:6
And Saul said unto the Kenites, Go, depart, get you down from among the Amalekites, lest I destroy you with them: for ye shewed kindness to all the children of Israel, when they came up out of Egypt. So the Kenites departed from among the Amalekites.
The verse belongs to the account of Saul's campaign against Amalek. The judgment on Amalek came because they had first attacked Israel in the wilderness and had persisted in opposing God and practicing idolatry, with the sentence against them delayed for four hundred years before its execution. Before striking, Saul told the Kenites to depart and get down from among the Amalekites lest they be destroyed with them, and the Kenites departed from among the Amalekites and were spared.
He spared them because they had shown kindness to all the children of Israel when Israel came up out of Egypt, so their past help was remembered amid the judgment. Yet Saul failed to fully carry out God's command to strike Amalek and destroy them. His protection of the Kenites stands in contrast to that failure against Amalek. That failure is an example of neglected duty that brought God's wrath.