Nǐ bùnénɡ yǐmàoqǔrén.
你不能以貌取人。
You can't judge a book by its cover.
Notes:
你(nǐ): you
不能(bùnénɡ): can't
以(yǐ): with
貌(mào): appearance
取(qǔ): to judge
人(rén): person, people
Example:
A:我不喜欢他。
Wò bù xǐhuān tā.
I don't like him.
B:你不能以貌取人。
Nǐ bùnénɡ yǐmàoqǔrén.
You can't judge a book by its cover.