A video released on Saturday knife attack in London Tube has been widely celebrated on social media. The video that uploaded to Twitter shows police restraining a man believed to be the attacker, while an onlooker can be heard shouting: "You ain't no Muslim bruv."

The defiant phrase created a quick trending in Twitter under #YouAintNoMuslimBruv. Many British Muslims have welcomed it through responses like “#YouAintNoMuslimBruv makes me proud to be a British Muslim” and “This is not what Islam teaches”.

Police were called to the East London station after reports of a stabbing in the ticket hall at around 7 p.m. on Saturday evening.

Accordingly, the officers arrested a 29-year-old man and said they are treating the "violent unprovoked knife attack" at east London's Leytonstone subway station as a "terrorist incident."

Scotland Yard's counter-terrorism command said on Sunday that it had opened an investigation into the incident.

The force said the decision was made because of information received from witnesses and subsequent police investigations. It said it was searching a residential address in east London, but declined to say whether they were looking for other suspects.

In Saturday's attack, one man suffered serious knife injuries and was in the hospital in stable condition. Another man received minor injuries, while a woman was threatened but not hurt.

Video shot by witnesses at the scene showed a pool of blood on the station's floor as the suspect – who was reportedly screaming “This is for Syria” when attacked his victims – was seen lunging at several police officers who tried to subdue him. He was then pinned down after a stun gun was used.