From Dale Gieringer, head of California NORML:
It was investigated by a Lincoln scholar at the request of Ollie Steinberg of the Minnesota Grassroots party. Like Mark, he found no record of any speech by Lincoln on the alleged date (Dec 18, 1840).
I've been told that according to the Home Book of Quotations (16th edition), it was fabricated in the 1880s - apparently by anti-Prohibitionists in Atlanta courting the Negro vote. Lincoln was well-known for his temperance sympathies. According to Herbert Asbury's "The Great Illusion," he authored a dry law modeled on the Maine law, which was rejected by Illinois voters in a special referendum on June 4, 1855. He was also alleged to have authored and signed a total abstinence pledge in 1846. According to temperance authorities, Lincoln was reluctant to sign the 1862 whiskey tax that helped fund the Civil War, on grounds it would condone the liquor trade. According to a temperance leader who spoke with him on the day of his assassination, Lincoln predicted that the next great question after slavery would be abolition of the traffic in legalized liquor.
I'm sorry to say that the Lincoln quote seems bogus, since I had it printed on California NORML's matchbooks. It's so good, I feel tempted to quote it as "attributed to Lincoln."