This form of the headword verb (present active infinitive) is largely attested in tragedy and commentary thereto. The most likely focus of this commentary is perhaps Sophocles, Ajax 432 (web address 1), which is also quoted at alphaiota 91 and delta 1701. See also line 904 of that play, and Euripides, Medea 1347.
For a related noun see alphaiota 3.
[1] Like in Erotian and elsewhere; similarly in Hesychius.
[2] Likewise in the Synagoge.