Hmm, well there's Ethics of the Father's 1:13: דִלָא מוֹסִיף יָסֵף, and 2:15 (slightly out of context): אָרוּן שֶל־חֲכָמִים; but neither of those quite seem to encapsulate what I'm after. Perhaps something from Proverbs, 3:13, for instance: אַשְׁרֵי אָדָם מָצָא חָכְמָה, וְאָדָם יָפִיק תְּבוּנָה. Or 9:9: תֵּן לְחָכָם, וְיֶחְכַּם-עוֹד; הוֹדַע לְצַדִּיק, וְיוֹסֶף לֶקַח. More anon. Such as when I can be bothered to skim the rest of the Book of Proverbs. :o)