From the scholia to Aristophanes, Acharnians 10, where the hero Dikaiopolis, recounting some recent experiences of pleasure and pain, recalls how at a recent theatrical festival he was "open-mouthed" (i.e. agog) in anticipation of watching a revival of a play of Aeschylus (alphaiota 357), only to be stunned when the herald announced one by Theognis (theta 137). The verb is the pluperfect of xa/skw (cf. kappa 1461, kappa 1462, kappa 1463, kappa 1464, kappa 1466, kappa 1467) and should therefore have an augment; editors accordingly print 'kexh/nh in Aristophanes' text, assuming that the augment underwent prodelision after the final long vowel of the preceding word dh\, and several ancient grammarians cite the verb in the full form e)kexh/nh.
[1] The fullest version of the Aristophanic scholium (in codd. E*g) notes that kexh/nea is an Ionic form. It is not actually attested, but other 1st person singular pluperfects of similar formation are, e.g. h)/|dea "I knew" (Homer, Iliad 14.71; Herodotos 2.150)