Father-of-three Zakariya Islam was killed at the Ruqya Therapy Centre’s based in Whitechapel.
Police and paramedics rushed to the scene and found the married 46-year-old Islamic healer suffering critical injuries.
Despite desperate attempts he could not be saved and was pronounced dead a short time later.
A 43-year-old man was arrested at the scene on suspicion of murder. He was treated in hospital for hand injuries and being questioned by detectives who recovered a knife following the attack at 6.30pm on Tuesday.
Mr Islam was a co-founder of the Ruqya centre, based in a complex of small business offices in Greatorex Street, and had been treating people who believe themselves possessed by ‘jinns’, or spirit, and black magic for more than a decade.
One of Mr Islam’s three daughters today said they were “in shock” and too distraught to speak about the tragedy.
His sister-in-law Shazeda Khanom, 41, said they could not believe what had happened.
She said: “He was a very nice man and we don’t know who would do something like this or have any reason to.”
A Met Police spokesman confirmed the victim and suspect were known to each other.
Mr Islam, from Mile End, was a former caretaker at Stepney Green Secondary School and a member of Islamic Forum of Europe.
Friends described him as a “popular guy with a big heart” who was well-known within the Muslim community.
One wrote online: “RIP Brother Zakariya Islam who was stabbed to death today near East London Mosque. It’s crazy to think how quickly someone’s life can be taken away.
“But as a result of such a brutal act. It just doesn’t seem fair.”
Mozahid Hussein, 46, a friend from childhood, said: “I saw him three days ago and we were laughing and joking. He was a loving person, full of energy. Even last week we were talking about our businesses.
“The whole of East London will be in shock. His humour was brilliant. He grew up around here and we played football together as children.
“He was someone you could go to for business advice. He was well respected. I never knew him to argue with anyone. He would listen to you and make you feel special.”
Neighbour Alam Ali, 28, said: “He was a normal guy and family man. I went to his daughter’s wedding and he was a wonderful man. His daughter only got married last month so it’s very unfortunate because this was a happy time for the family.
“Everyone’s just in shock about it.”
Zayd ul Islam, a friend who lives in the UAE, called it a “heinous crime”.
Writing on Facebook, he paid tribute to “our dear brother”, calling him a “great individual”.
He said: “The sadness cannot be described. Zakariya was known to many for his honesty, piety, warmth, love and his long term work of helping people.
“He leaves a beautiful family behind and we pray for them.”
Tasawer Islam, who also works at the Ruqya centre running “distance healing treatment”, wrote: “He was friend, a teacher and a great helper and supporter. He will be missed by many.”
The Metropolitan Police said in a statement, “At this early stage it is believed that the victim and suspect were known to each other. Detectives are not looking for anyone else in connection with this incident. Detective Inspector John Marriott from the Homicide and Major Crime Command leads the investigation.” A newspaper quoted.
Another friend, who wished to remain anonymous, agreed the only explanation for the stabbing was a disgruntled client, quoted a newspaper.
“The rumor is that it was a client that thought he had been given bad advice and then attacked him,” he told the Daily Mail.
“He was a good man and really well-known in the community.”