This depiction of The Youthful David (note also the head of Goliath) is by Andrea del Castagno (
source). The verse is 1Sam 17:51.
ἐθανάτωσεν αὐτὸν καὶ ἀφεῖλεν τὴν κεφαλὴν αὐτοῦ
interfecit eum, praeciditque caput eius.
He slew him and cut off his head.
