"The better part of valor is discretion" is from which play written by William Shakespeare?

In William Shakespeare's play Henry IV, Part I - Act 5, scene 4, 115–121, Falstaff is present in the scene and he says: "To die is to be a counterfeit, for he is but the counterfeit of a man who hath not the life of a man; but to counterfeit dying, when a man thereby liveth, is to be no counterfeit, but the true and perfect image of life indeed. The better part of valor is discretion, in the which better part I have sav'd my life." It is clear that the idea is to use caution and not become involved in rash bravery. It is better to be prudent than merely courageous; 'discretion is the better part of valor' as the quote is mostly stated.

In the play, Falstaff is hinting that he has hidden or even played dead when on a battlefield. He did this in order to avoid any personal danger to himself or others. Falstaff believed that he was using proper judgment over any unwarranted bravery. He had to exercise caution. He wouldn't take unnecessary risks! This is what he always saw smart people like himself doing.