After a lengthy hearing on Tuesday, a disciplinary panel found Ashton guilty of biting Waller during Saracens' 27-12 win in the Premiership on Saturday.
Ashton contested two counts of biting, but was found guilty of one and banned for 13 weeks.
He is free to play again on Dec. 19.
"Having considered detailed evidence the panel concluded that during the course of a ruck Chris Ashton bit the arm of Alex Waller at a time that Mr Waller was attempting to clear him out," Philip Evans QC, chairman of the disciplinary panel, said.
