PROS KORINQIOUS B, chapter 1 31:

εἰ γὰρ ἐγὼ λυπῶ ὑμᾶσ, καὶ τίσ ὁ εὐφραίνων με εἰ μὴ ὁ λυπούμενοσ ἐξ ἐμοῦ;