In my native language, when we hear someone ask if it's a good idea to do something good for the sake of others, we say, "need one ask to do a good act?". It means doing a good thing for others, or being kind to them, needs no conditions or any questions to be answered - just go ahead and do it.
Sometimes it's used humorously to accept an offer when someone offers you something, e.g. your friend offers you some cookies and says, "Want some?" And you respond, "Need one ask to do a good act?"
Is there any English equivalent of this proverb for both contexts that I described above?