"Madness in great ones must not unwatched go" is from which play by William Shakespeare?

In William Shakespeare play "Hamlet", king Claudus states "madness in great ones must not unwatched go". Scholars have said that here the king is pointing out a specific meaning. When one is confronted with madness, he or she must consider the person and what they may be thinking.

In Act 3, scene 1 of the play, the quote ("madness in great ones must not unwatched go") is stated by King Claudius after overhearing Hamlet's denial of Ophelia's love. Some dramatic irony takes place because Claudius is referring to Hamlet but in reality he is also referring to himself. Claudius comes to believe that he really shouldn't have murdered Hamlet's father and married his widow, Hamlet's mother. Was he mad when committed the murder?