Siva,

     According to the sixteenth edition of BARTLETT'S FAMILIAR QUOTATIONS,
the quote is attributed to the prolific "Anonymous."  Since Twain scholar
Justin Kaplan edited the volume, it is compelling evidence that Twain never
said it.

     Here is a sampling of things Twain *did* say about good deeds:

>From WHAT IS MAN?:

   Y.M. It is my opinion that under your scheme
of a man's doing a good deed for his OWN sake
first-off, instead of first for the GOOD DEED'S
sake, no man would ever do one.

>From "Some Rambling Notes of an Idle Excursion::

That's the way I felt about it.  Says I, what's a dollar, any way?
Life's on'y a pilgrimage, says I; we ain't here for good, and we
can't take it with us, says I.  So I just dumped it down, knowin'
the Lord don't suffer a good deed to go for nothin', and cal'latin'
to take it out o' somebody in the course o' trade.

>From HUCK FINN:

Pap always said, take a chicken when you get a chance, because if
you don't want him yourself you can easy find somebody that does,
and a good deed ain't ever forgot. I never see pap when he didn't
want the chicken himself, but that is what he used to say, anyway.

Kevin B.