"The fool doth think he is wise, but the wise man knows himself to be a fool" comes from which play of Shakespeare?

In the William Shakespeare play, "As You Like It" in Act 5, Scene 1, Touchstone says to William:

"Why, thou sayst well. I do now remember a saying: “The fool doth think he is wise, but the wise man knows himself to be a fool.” The heathen philosopher, when he had a desire to eat a grape, would open his lips when he put it into his mouth, meaning thereby that grapes were made to eat and lips to open. You do love this maid?"

William: I do, sir.

Touchstone: Give me your hand. Art thou learned?

William: No, sir.

Thus, looking at these two men, critics and scholars who have interpreted this scene and the above words in "As You Like It," hold that the meaning is clear. It points out that the fool is ignorant and thinks he knows everything. The wise man continues to search for knowledge, searching for knowledge is a never ending quest. A person should always want to know more. The more you see and experience, the less you know, then you'll learn.