What is the Buddha?

A monk asked Master Chao-chou: “What is the Buddha?” The master replied: “The one in the hall.” The monk said, “But the one in the hall is an image, a mere statue, a lump of mud.” Chao-chou agreed, “That’s true.” “So,” persisted the monk, “what is the Buddha?” Chao-chou responded: “The one in the hall!”