The Iliad 5.825

And the goddess, flashing-eyed Athene, answered him, saying: Son of Tydeus, Diomedes, dear to my heart, fear thou not Ares for that, neither any other of the immortals; so present a helper am I to thee. Nay, come, at Ares first drive thou thy single-hooved horses,and smite him in close fight, neither have thou awe of furious Ares that raveth here a full-wrought bane, a renegade, that but now spake with me and Hera, and made as though he would fight against the Trojans but give aid to the Argives; yet now he consorteth with the Trojans and hath forgotten these.