"He is on a life support system since his condition is very critical," former Supreme Court judge Ashok Ganguly, who was present at the hospital, told PTI.
"He is suffering from a kidney-related ailment," Justice (retd) Ganguly, also a close friend of Justice (retd) Kabir, said.
"He is in a critical condition and is undergoing treatment," spokesperson of Apollo Hospitals Anjali Singh said.
Kabir, 68, was appointed the 39th Chief Justice of India on September 29, 2012, a post he held for 292 days, before his retirement on July 19, 2013.