"Twain probably never uttered [these] words," according to R. Kent Rasmussen, editor of The Quotable Mark Twain (1998). <br class="br">"To play golf is to spoil an otherwise enjoyable walk" is found in H.S. Scrivener, "Memories of Men and Meetings" https://books.google.com/books?id=cYgCAAAAYAAJ&q=dicta#v=snippet&q=dicta&f=false, in Arthur Wallis Myers (ed.) Lawn Tennis at Home and Abroad New York:Charles Scribner’s Sons, 1903, p. 47. Scrivener attributes the aphorism to "my good friends the Allens". Reference from Quote Investigator http://quoteinvestigator.com/2010/05/28/golf-good-walk. <br class="br">Misattributed

“She had run down and down and down, and had at last reached a point where medicines no longer had any helpful effect upon her. I said I knew I could put her upon her feet in a week. It brightened her up, it filled her with hope, and she said she would do everything I told her to do. So I said she must stop swearing and drinking, and smoking and eating for four days, and then she would be all right again. And it would have happened just so, I know it; but she said she could not stop swearing, and smoking, and drinking, because she had never done those things. So there it was. She had neglected her habits, and hadn’t any. Now that they would have come good, there were none in stock. She had nothing to fall back on. She was a sinking vessel, with no freight in her to throw overboard and lighten ship withal.”

Mark Twain book Following the Equator

Source: Following the Equator (1897), Ch. I

“We haven't all had the good fortune to be ladies; we haven't all been generals, or poets, or statesmen; but when the toast works down to the babies, we stand on common ground.”

Mark Twain

Answering a toast, "To the Babies," at a banquet in honor of General U.S. Grant (November 14, 1879). <br class="br">The Writings of Mark Twain, Vol. 20 (1899), ed. Charles Dudley Warner, p. 397 http://books.google.com/books?id=mRARAAAAYAAJ&pg=PA397

“The Erie railroad kills 23 to 46; the other 845 railroads kill an average of one-third of a man each; and the rest of that million, amounting in the aggregate to that appalling figure of 987,631 corpses, die naturally in their beds! You will excuse me from taking any more chances on those beds. The railroads are good enough for me.”

Mark Twain

"The Danger of Lying in Bed" (1871)

“It does look as if Massachusetts were in a fair way to embarrass me with kindnesses this year. In the first place, a Massachusetts judge has just decided in open court that a Boston publisher may sell, not only his own property in a free and unfettered way, but also may as freely sell property which does not belong to him but to me; property which he has not bought and which I have not sold. Under this ruling I am now advertising that judge's homestead for sale, and, if I make as good a sum out of it as I expect, I shall go on and sell out the rest of his property.”

Mark Twain

Letter of acceptance of membership to Concord Free Trade Club (March 28, 1885): Mark Twain, his life and work: a biographical sketch (1892), William Montgomery Clemens, Clemens Pub. Co.

“"In God We Trust." Now then, after that legend had remained there forty years or so, unchallenged and doing no harm to anybody, the President suddenly "threw a fit" the other day, as the popular expression goes, and ordered that remark to be removed from our coinage.
Mr. Carnegie granted that the matter was not of consequence, that a coin had just exactly the same value without the legend as with it, and he said he had no fault to find with Mr. Roosevelt's action but only with his expressed reasons for the act. The President had ordered the suppression of that motto because a coin carried the name of God into improper places, and this was a profanation of the Holy Name. Carnegie said the name of God is used to being carried into improper places everywhere and all the time, and that he thought the President's reasoning rather weak and poor.
I thought the same, and said, "But that is just like the President. If you will notice, he is very much in the habit of furnishing a poor reason for his acts while there is an excellent reason staring him in the face, which he overlooks. There was a good reason for removing that motto; there was, indeed, an unassailably good reason — in the fact that the motto stated a lie. If this nation has ever trusted in God, that time has gone by; for nearly half a century almost its entire trust has been in the Republican party and the dollar–mainly the dollar. I recognize that I am only making an assertion and furnishing no proof; I am sorry, but this is a habit of mine; sorry also that I am not alone in it; everybody seems to have this disease.
Take an instance: the removal of the motto fetched out a clamor from the pulpit; little groups and small conventions of clergymen gathered themselves together all over the country, and one of these little groups, consisting of twenty-two ministers, put up a prodigious assertion unbacked by any quoted statistics and passed it unanimously in the form of a resolution: the assertion, to wit, that this is a Christian country. Why, Carnegie, so is hell. Those clergymen know that, inasmuch as "Strait is the way and narrow is the gate, and few — few — are they that enter in thereat" has had the natural effect of making hell the only really prominent Christian community in any of the worlds; but we don't brag of this and certainly it is not proper to brag and boast that America is a Christian country when we all know that certainly five-sixths of our population could not enter in at the narrow gate.”

Mark Twain

Statements (c. December 1907), in Mark Twain In Eruption : Hitherto Unpublished Pages About Men And Events (1940) edited by Bernard Augustine De Voto

“These facts are all on the credit side of the proposition that the Jew is a good and orderly citizen. Summed up, they certify that he is quiet, peaceable, industrious, unaddicted to high crimes and brutal dispositions; that his family life is commendable; that he is not a burden upon public charities; that he is not a beggar; that in benevolence he is above the reach of competition. These are the very quintessentials of good citizenship.”

Mark Twain book Concerning the Jews

Concerning the Jews (Harper's Magazine, Sept. 1899)

“The bicycle had what is called the 'wabbles', and had them very badly. In order to keep my position, a good many things were required of me, and in every instance the thing required was against nature. Against nature, but not against the laws of nature.”

Mark Twain

"Taming the Bicycle" (1917)

“Persons who think there is no such thing as luck—good or bad—are entitled to their opinion, although I think they ought to be shot for it.”

Mark Twain

Source: Autobiography of Mark Twain, Volume 1 (2010), p. 380