A police officer stood guard outside Leytonstone station in north London Sunday, a day after three people were stabbed in what police are treating as a "terrorist incident." AFP/Getty Images

Within hours of a Saturday stabbing in the London underground that injured three people, the Twitter hashtag "You Ain’t No Muslim, Bruv" began trending. Police are investigating the incident as a terrorist attack, and the hashtag was inspired after a video surfaced showing a man in the station shouting the phrase as the suspect was being arrested.

The suspect, a 29-year-old man, allegedly entered the Leytonstone subway in east London around 7 p.m. local time and stabbed three people while shouting, "This is for Syria." One 56-year-old man was seriously injured in the attack.

As the suspect was being detained by the police, one man can be heard shouting "You ain't no Muslim, bruv" at the alleged attacker in a video posted to YouTube. "Bruv" is British slang similar to the U.S. term "bro," and the phrase was soon picked up by social media users to address the problem of identifying all Muslims with Islamic extremists. Instances of discrimination against Muslims have risen in the weeks following a spate of terror attacks in Paris as well as a suspected terrorist massacre in San Bernardino, California, tied to radicalization.

"You obviously don't even know what the word 'Islam’ stands for," tweeted one user, who identified as a script writer and filmmaker and was wearing a hijab or headscarf in her user photo. "This isn't a religion problem; it's a human problem," tweeted another user.

By Sunday nearly 100,000 posts on Twitter featured the hashtag.

The response on social media came as local authorities warned of more possible attacks. "I would continue to urge the public to remain calm but alert and vigilant,” said Commander Richard Walton of the counterterrorism unit, as reported by the BBC. He added, “The threat from terrorism remains at severe, which means that a terrorist attack is highly likely."