From Liu Yuxi's (
刘禹锡) Tang classical essay 《
陋室铭》 (Inscription for a Humble Room):
谈笑有鸿儒,
往来无白丁。 — 'Those who laugh with me are great scholars; those who come and go include no commoners.'
白丁 = an uneducated commoner (originally a man of humble rank without official posting). A standard middle-school text.