Which William Shakespeare play has the phrase: "Thus conscience does make cowards of us all"?

This sentence (line) is from Hamlet and is part of his soliloquy from Act 3, scene 1. It is part of the single most famous speech in Hamlet. The focus here is on what Hamlet is thinking. He has questions. They are asked in the soliloquy. A few specific questions are: Is he cowardly? Has he given up on life? Is he seriously contemplating suicide or is he just waxing philosophical? Deliberating over the truth or falsehood of what the Ghost has told him? Making sure he has all his ducks in a row, all his i’s dotted and t’s crossed? The answers may never be known.