Advice

Aeschylus, Prometheus Bound 327-329 (Oceanus to Prometheus; tr. Alan H. Sommerstein):

You keep quiet and don't speak too impetuously;
or do you not know very well, exceptionally intelligent as you
are, that foolish words lead to punishment being inflicted?

σὺ δ᾿ ἡσύχαζε μηδ᾿ ἄγαν λαβροστόμει.
ἢ οὐκ οἶσθ᾿ ἀκριβῶς, ὢν περισσόφρων, ὅτι
γλώσσῃ ματαίᾳ ζημία προστρίβεται;

λαβροστόμει is a hapax legomenon. Joseph Edward Harry ad loc.: