Source, in full
According to the book, "They Never Said It", p. 64, there is no evidence Lenin ever said this. Lenin was supposed to have made his observation to one of his close associates, Grigori Zinoviev, not long after a meeting of the Politburo in the early 1920s, but there is no evidence that he ever did. Experts on the Soviet Union reject the rope quote as spurious. However, it may confusedly derive as paraphrase from chapter 9 of Lenin's ""Left-Wing" Communism: an Infantile Disorder" (1920), but this version contains no mention of selling, and refers instead to politicians with a given relation to capitalism
Notes from Wikiquote
"[W]ith my vote, I want to support Henderson in the same way as the rope supports a hanged man—that the impending establishment of a government of the Hendersons will prove that I am right, will bring the masses over to my side, and will hasten the political death of the Hendersons and the Snowdens just as was the case with their kindred spirits in Russia and Germany."