Doing a job before knowing about the price offered

What is the ruling if a person does a job, then finds out that the one who wanted it done said “Whoever does such and such will have such and such”?

Praise be to Allah, and blessings and peace be upon the Messenger of Allah:

If he does it before finding out that the one who wanted it done said “Whoever does such and such will have such and such” does not deserve the price named. But it is good manners to give him something that will please him, that is similar to or more than the price for this work.