ταῦτ' ἐπίστω καὶ γράφου φρενῶν ἔσω

From LSJ

ἔσῃ γὰρ ὡς πετεινοῦ ἀνιπταμένου νεοσσὸς ἀφῃρημένος → for you will be as a nestling taken away from a bird that is flying

Source