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

Shakespeare or whoever he was called was a genious. Been to his house in Stradford-upon-Avon and in the renewed Globe Theatre in London, England. He was probably well travelled or had a friend who was well travelled in Europe ...

I have an old 78rpm record of Sir Lawrence Olivier giving this speech from the film. On the flip side is Oh that this too, too solid flesh... I love Shakespeare.