In Act II, Scene 2, when Macbeth enters still holding two bloody daggers and with both hands covered in blood, Lady Macbeth directs the audience's attention to the daggers and blood:
Go, get some water
And wash this filthy witness from your hand.
Why did you bring these daggers from the place?
They must lie there. Go carry them, and smear
The sleepy grooms with blood.
But she is forced to carry out her own instructions, since her husband refuses to do so. He tells her:
I'll go no more:
I am afraid to think what I have done;
Look on't again I dare not.
When she leaves, Macbeth looks at his bloody hands and speaks the following:
Will all great Neptune's ocean wash this blood
Clean from my hand? No, this my hand will rather
The multitudinous seas incarnadine,
Making the green one red.
Here, "suiting the action to the word, the word to the action," the hallucinating Macbeth is presumably attempting to wash his hands in a conveniently situated basin. He imagines that he is failing to wash them, even in all the world's oceans, because his hands are so bloody. When Lady Macbeth reenters, she notices that her husband's hands are still covered with blood. She displays her own-now bloody hands and says:
My hands are of your color, but I shame
To wear a heart so white.
Presumably, Macbeth, continuously hallucinating, had tried to wash his hands in an empty wash-basin. His wife explains this to the audience by saying:
Hath left you unattended....
Be not lost
So poorly in your thoughts.