LSJ
aor. imper. of *σπῶ, = λέγω, EM 740.11 (mentioned without expl. by A.D. Adv. 147.1); pl. σπέτε, = εἴπατε, Hsch.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
Pape
imperat. zu εἰπεῖν statt εἰπέ, EM. Vgl.
Pape, Griechisch-deutsches Handwörterbuch (3. Aufl., 1914)