Plutarch, Platonicae quaestiones, chapter 7, section 7 4:

πῶσ οὖν οὔτε λίθον οὔτε ξύλον ὁ ἀὴρ ἀλλὰ μόνον τὸν σίδηρον ὠθεῖ καὶ προστέλλει πρὸσ τὴν λίθον;