Epictetus – Enchiridion CXLII
Nature has given to men one tongue, but two ears, that we may hear from others twice as much as we speak.
La Rochfoucauld – Collected Maxims V:142
As great minds have the ability to say much in few words, so, conversely, small minds have the gift of talking much and not saying anything.
Attributed to Plato, but origins likely unknown
Wise men talk because they have something to say; fools, because they have to say something.
Plutarch – On Listening
Anyone who has acquired the ability to listen in a self-controlled and respectful fashion is receptive to and retentive of any remarks that are useful, while any that are useless or false are quite transparent to him and easily detectable, because he is–as is obvious–aiming at the truth rather than at winning an argument, and does not pitch in head first for a fight.