"People of Delhi might not know that last year he (Kejriwal) went to his office only for two days," Mishra alleged in a letter to the Chief Minister.
"Does Kejriwal have the guts to show his performance report to the people of Delhi?"
Mishra also described Kejriwal as the only Chief Minister in the country without any portfolio and "who hardly works".
"Kejriwal is the Chief Minister who takes maximum holidays and now he shall soon become the Chief Minister against whom maximum cases of corruption would be there," the sacked minister said.
Mishra also dared Kejriwal to prove any one of his allegations wrong.
"Open challenge to Kejriwal, at least prove one allegation wrong. I have written about you only," he said.
Mishra was sacked as the Water, Tourism and Culture Minister on May 6 following internal bickering in the ruling party.