Complete: "Man sees the outward appearance, but the LORD sees the…"

Answer: Heart

God said this when Samuel was impressed by Jesse's son Eliab, whose appearance and height had not made him the LORD's choice.

“When they arrived, Samuel saw Eliab and said, “Surely here before the LORD is His anointed.” But the LORD said to Samuel, “Do not consider his appearance or height, for I have rejected him; the LORD does not see as man does. For man sees the outward appearance, but the LORD sees the heart.””— 1 Samuel 16:6-7 (BSB)