Per its title, Psalm 54 was written when which people told Saul that David was hiding among them?

Answer: The Ziphites

Its title: "When the Ziphites went to Saul and said, 'Is David not hiding among us?'" The psalm then prays, "Save me, O God."

“For the choirmaster. With stringed instruments. A Maskil of David. When the Ziphites went to Saul and said, “Is David not hiding among us?” Save me, O God, by Your name, and vindicate me by Your might!”— Psalm 54:1 (BSB)