Euripides, Herakleidai 939-940

“For it is the sweetest thing to see an enemy who is plagued by misfortune after enjoying prosperity.”

…ἐκ γὰρ εὐτυχοῦς
ἥδιστον ἐχθρὸν ἄνδρα δυστυχοῦνθ’ ὁρᾶν.