This could be in Simple Questions.

The only persons who seem to believe this are TV political commentator Bill O'Reilly and co-author Martin Dugard, who wrote a book positing that Stalin had Patton killed so he wouldn't resist the Russian takeover of eastern Europe. The National WW2 Museum ( hardly a Soviet Union sympathizer) has a good article on Patton's death here. One excerpt:

Patton was rushed to the 130th Station Hospital in Heidelberg, 12 miles away. There, he was x-rayed, revealing two crushed vertebrae. Simply put: Patton had broken his neck. For the next 12 days, Patton lay in traction, at times with painful fishhooks implanted into his cheeks on either side of his upper jaw, attached to weights to stabilize his neck. His wife, Beatrice, flew in from Boston to be at his side and read him books and letters from well-wishers. Showing a few signs of recovery, his doctors put him in a body cast to prepare him for a flight home to the United States. Unfortunately, he succumbed to his paralysis and breathed his last before the move could be made. <

There's no evidence Patton was poisoned. There's also no evidence that, say, operatives sent by Chou En Lai killed him so he wouldn't stop the CCP takeover of China after the war, or that Charles Lindbergh , working for the Nazis, had him killed. But the standard method for advancing these conspiracy theories is to burden your opponents with the task of finding facts that contradict the theory- try to prove that Stalin or Chou En Lai or Lindbergh could never have done it. But the burden of proof should always be on the theorist. How could I ask you to prove I did not see an elephant in my yard yesterday? You should instead be able to ask me to prove that I did. Why should we not believe that Patton died from the logical consequences of breaking his neck?

It's even possible the authors don't believe it, either: they only want to peddle a saleable conspiracy theory about the assassination of a famous general by leftist traitors. O'Reilly no doubt has a sizeable conservative audience who'd love to think this. If you can discern an audience who'd love to think Chou En Lai or Lindbergh did it, to my knowledge that book has not been written. An opportunity awaits....