It's the first of the month, and I need some good luck.
The exact origin of the superstition is unknown, though it was recorded in Notes and Queries as being said by children in 1909...
"When I was a very little boy I was advised to always murmur 'White rabbits' on the first of every month if I wanted to be lucky. From sheer force of unreasoning habit I do it still—when I think of it. I know it to be preposterously ludicrous, but that does not deter me." – Sir Herbert Russell, 1925.
"Even Mr. Roosevelt, the President of the United States, has confessed to a friend that he says 'Rabbits' on the first of every month—and, what is more, he would not think of omitting the utterance on any account." – newspaper article, 1935.
Addendum: Isolated track of Grace Slick's vocal ("What a voice. As noted, the reverb is from recording in an empty room, but the vibrato is pure Grace.")