What does macbeth say when he is talking about evil grows stronger with more evil? Provide quote

I'm not sure where you are in the play exactly. Macbeth alludes to this many times throughout the play. In Act 3 scene 4 he says, "I am in blood Stepp’d in so far that, should I wade no more, Returning were as tedious as go o’er." If yo can give me a scene you are sure about, that would be better.

I know for sure it's not scene three but I'm not sure if its scene one or two

In act 3 scene 2 Macbeth gives this rather cryptic message to his wife,

"Things bad begun make strong themselves by ill.

So, prithee, go with me."

Basically he is saying that evil grows stronger with more evil.