The story
Originated with the Black Panther Party. One of the variations of the proverb formula scratch (somebody) and you'll find (somebody else). Compare for example Russian поскреби русского - найдёшь татарина (poskrebi russkovo - najdjóšʹ tatarina, “scratch a Russian and you'll find a Tatar”).
Etymology from Wiktionary, CC BY-SA 4.0.