Making an emotive appeal to tens of thousands gathered at the Gandhi Maidan here, the Gujarat chief minister called upon the people of Bihar to "punish" Nitish Kumar in the next election.
Modi, who described Nitish Kumar as a friend, said he was not surprised when the chief minister and the Janata Dal-United ended the alliance with the Bharatiya Janata Party in Bihar in June.
"If my friend (Nitish Kumar) can "betray JP" (Jaya Prakash Narayan), then he could certainly "betray" the BJP too.
It was first time Modi directly attacked Nitish Kumar by calling him an opportunist.
"Nitish Kumar is a 'chela' of Lohia and JP, both of who fought the Congress all through their lives. But Nitish Kumar back-stabbed them by playing into the hands of the Congress."
Modi said voters would not forgive him for joining hands with the Congress.
Modi also accused Nitish Kumar of playing "dirty politics" to stop him from visiting Bihar.
"Several times I was stopped from visiting Bihar. But I tolerated the insult for the sake of Bihar."
Modi also recalled how he was humiliated in 2010 when Nitish Kumar cancelled a dinner for him and other BJP leaders. "I did not react for the sake of keeping Bihar free from jungle raj."
Modi roared that it was the BJP which made Nitish Kumar the Bihar chief minister in 2000 for seven days and again in 2005.
--IANS (Posted on 27-10-2013)