Kasparov - Nakamura. The Touch Incident
Watch the moment:
Kasparov played his knight from d5 to b4 left his hand, suddenly noticed that 27.Bc5! would lose the game. So he picked his knight again and moved it to f4. "I was not sure whether I had left the knight. In blitz it is difficult to tell," said Garry in his interview with Maurice Ashley at the end of the day. "I looked at Hikaru and the arbiter. If they would have claimed I would have resigned the game."