Let's see if I can support that claim to your satisfaction. 

According to Webster's, classification is “a systematic arrangement into groups or categories according to established criteria.” And prejudice is “an opinion or leaning adverse to something without just grounds or before sufficient knowledge.” 

Of Webster's two conditions for prejudice — the absence of just grounds and the sufficient knowledge — the first is sheer nonsense. Everyone who is prejudiced against someone of another race believes he has just grounds for feeling that way. So let's throw that one out and keep only the other one. 

Now if you put the two ideas together — the idea of classifying people into groups or categories and the idea of holding an adverse opinion of someone before you've gotten to know him — it's patently obvious that you can't be racially prejudiced against anyone you've gotten to know unless you ignore everything you know about him except the racial class into which you've placed him. 

Now you may not like him. But you can't be prejudiced against him. 

So here's what I suggest. 

The next time you run into someone you don't know, try not to think, “He's a black.” Or “He's a white.“  Or “He's an Oriental.“ Or some such thing. Try to think instead, “His skin is darker than mine.“ Or “His skin is lighter than mine.“ Or “His skin is more yellow than mine.“ You'll be amazed at how differently you'll feel towards him right off the bat. And as you get to know him, the whole idea of his race will recede further and further until it disappears. 

Try it. I know it works ‘cause I've done it. 

Think about it.