Saying versus doing

"But what do you think? A man had two sons, and he came to the first and said, 'Son, go work today in the vineyard.'

And he answered, 'I will not'; but afterward, he regretted it and went.

The man came to the second and said the same thing; and he answered, 'I will, sir'; but he did not go.

Which of the two did the will of his father?"

--Matthew 21:28-31a