Aelian, On The Nature of Animals 3.41
“India gives birth to single-horned horses, people say, and the same land feeds single-horned asses too. They get drinking cups from these horns. And if anyone puts fatal poison inside of them, when someone drinks from them, the conspiracy won’t hurt him at all. It seems that the horn of both the horse and the ass is a ward against evil.”
Ἵππους μονόκερως γῆ Ἰνδικὴ τίκτει, φασί, καὶ ὄνους μονόκερως ἡ αὐτὴ τρέφει, καὶ γίνεταί γε ἐκ τῶν κεράτων τῶνδε ἐκπώματα. καὶ εἴ τις ἐς αὐτὰ ἐμβάλοι φάρμακον θανατηφόρον, ὁ πιών, οὐδὲν ἡ ἐπιβουλὴ λυπήσει αὐτόν· ἔοικε γὰρ ἀμυντήριον τοῦ κακοῦ τὸ κέρας καὶ τοῦ ἵππου καὶ τοῦ ὄνου εἶναι.