 "Anna Hazare congratulates Aam Aadmi CM Kejriwal")
He said he could not attend the swearing-in ceremony because of ill-health.
Hazare also wrote a letter to Kejriwal congratulating him and his Cabinet colleagues on taking charge of Delhi.
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"We have worked together for many years.... I congratulate you for taking the oath of Chief Minister today. I also congratulate others taking oath with you today," he told reporters at his village Ralegan Siddhi in Maharashtra.
45-year-old Kejriwal, whose AAP rewrote the grammar of politics in Delhi, was today sworn in as Chief Minister at the historic Ramlila Maidan in the national capital.
Hazare's massive rallies earlier calling for the passage of the Jan Lokpal Bill at the very same venue saw Kejriwal coming into limelight as a national anti-corruption champion before he took a plunge into mainstream politics calling for a "systemic change".
The new Chief Minister in his 20-minute speech invoked his mentor Hazare, who he said had labelled "politics as dirty".
"Annaji used to say that politics is dirty, but to clear the muck one has to enter the muck.... If we want to clean the system, then we will have to enter into this 'dirty politics'," Kejriwal said in Delhi.
The 76-year-old Gandhian invoking the holy text Gita suggested the new government serve the society and the country with a "selfless motive" and "not think of the results".
"The ultimate aim of politics is to serve ('seva')... To serve society, to serve the country, and 'seva' (service) means selfless service.
"Whatever one does in politics, do not think of the results and that is service and that is the worship of god," Hazare said.
Dressed in his usual aam aadmi avatar, Kejriwal in his speech promised to the people a "corruption-free government" and new style of governance without "arrogance of power".
"Kejrwal has not become CM today or these people have not become ministers today. That was not our aim. It is 1.5 crore people of Delhi whose government has been formed today," he said to a resounding applause at a jam-packed venue.
The two had parted ways last year when Kejriwal decided to form the AAP. Their ties has soured during the Delhi Assembly elections, when Hazare asked Kejriwal not to use his name in the campaign posters and pamphalets.