The incident was thought to have occurred in October 2010.
The nurse was feeding the patient when she was alleged to have hit her on the leg.
A witness told the tribunal she had heard the nurse say "for God's sake, will you bloody well keep still while I'm trying to feed you,'' or words to that effect.
Witnesses at the hearing in March 2013 told the tribunal that the patient was rarely known to sit still while the nurse fed her.
The patient had lashed out unintentionally before, and the tribunal found it was likely the nurse put her hand firmly on the patient's leg to keep her still while she fed her.
The difficulties of establishing proof when the patient communicated with a communication board, and had been asked leading questions, arose at the hearing.
The tribunal dismissed the charge.
The identity of the nurse, patient and institution are suppressed.