ἐπιστητέον
From LSJ
βωμὸν Ἀριστοτέλης ἱδρύσατο τόνδε Πλάτωνος, ἀνδρὸς ὃν οὐδ' αἰνεῖν τοῖσι κακοῖσι θέμις → Aristotle had this altar of Plato set up — Plato, a man whom the wicked dare not even mention in praise
English (LSJ)
A one must know, Sch.D.T.p.316H., An.Ox.3.207.
Greek (Liddell-Scott)
ἐπιστητέον: ῥημ. ἐπίθ. τοῦ ἐπίσταμαι, δεῖ ἐπίστασθαι, Ἀνέκδ. Κραμήρου τ. 3. σ. 207. 14, κτλ.