Nitish wrote: "Your statement about my DNA in your last rally, has left me and a large section of society deeply hurt. The choice of your words has not insulted the people of Bihar but also people living outside Bihar."
Kumar also added that 'such a statement has not been made for first time. "Earlier also BJP leader Nitin Gadkari said, 'casteism is in Bihar's DNA," he wrote.
Hitting back at Modi, Kumar wrote: "I am a son of Bihar. My DNA is similar as that of the people of Bihar." He posted a copy of the letter on his Twitter profile.