An onlooker shouted the phrase at the suspect as he was apprehended by police
Twitter users are making the hashtag #YouAintNoMuslimBruv trend to show their contempt for the the suspected Tube station terror attacker.
A man wielding a large knife apparently shouted "this is for Syria" during a stabbing attack at Leytonstone station in east London on Saturday night.
One victim was stabbed in the neck, leaving him seriously injured. His condition is reported not to be life-threatening. A second man received minor injuries.
Video footage shows police officers pinning the suspect to ground after Tasering him as a bystander shouts to him: "You're not a Muslim bruv, you're an embarrassment."
Social media users pounced on the phrase, with many praising the man who said it.
One user called Barneswallace wrote: "#YouAintNoMuslimBruv seems like the best response to terrorism ive heard for ---ever"
Alexander Edwards responded: "#YouAintNoMuslimBruv shouted by Muslims at the #Leytonstone attacker. Good on you lads!"
Another user, Azee, said: "The Lad who shouted #youaintnomuslimbruv deserves Nobel Peace Prize"
Chris Lowndes wrote: "#YouAintNoMuslimBruv is just perfect - real, inclusive, undermines terrorist cause."
Roy Kerr said: "This is so beautifully British. I hope the victim pulls through. #YouAintNoMuslimBruv"
Another called Jackie Nn wrote: "#youaintnomuslimbruv- soo proud to be a Londoner. True Muslims don't try and kill innocent bystanders. Peace to true Muslims."
Muthla wrote: "Best # trend I've seen- #YouAintNoMuslimBruv regarding horrific attack in Leytonstone. Gotta love London for the # trend!"
Matthew Harper said: "#youaintnomuslimbruv is the most #London response to terrorism you could imagine and pretty much sums up how we all feel about these maniacs."
The suspect, understood to be a 29-year-old man, is being questioned by police in east London after being taken into custody.