A Chennai-bound IndiGo plane received a threat message on Friday afternoon and the aircraft returned to the bay at the Delhi airport, according to sources.The aircraft did not take off.The Delhi-Chennai flight 6E 6091, to be operated with an A321 neo aircraft, was scheduled to depart at around 3.15 pm, as per information available on flight tracking website Flightradar24.com.Sources said the Air Traffic Controller (ATC) received a call regarding a threat message for the flight. In one of the lavatories of the aircraft, a message was found saying ‘Do not fly 6E 6091’, they added.It could not be immediately ascertained whether the message was found written on a paper or on the wall of the lavatory.The aircraft had pushed back and was preparing for takeoff. Following the message, it was decided to take the plane to the isolation bay for anti-sabotage checks, sources said.Details about the number of passengers could not be immediately ascertained.Comments from IndiGo were awaited.