"The decision was a difficult one to take. But the decision is final. Nitishji will resign. It is a decision in favour of the nation, the party and also Nitishji," said Yadav.
Meanwhile, Kumar himself will take a final decision on his resignation on Monday.
Kumar appeared to script a return as JD-U leaders on Sunday demanded his reinstatement in a crucial meeting, a day after his dramatic resignation following a poll debacle.
A closely-watched JD-U meeting ended in a logjam as leaders of the party failed to choose a new leader, almost unanimously backing Kumar, while the former Chief Minister himself did not budge on his call.
Kumar however placated his party leaders for now by telling them he needs another day to think about what they have told him.
"We were adamant there would be no other choice. Nitish ji said he needs another day so we have asked him to hold another meeting tomorrow," said JD-U leader Nitish Mishra.
Earlier in the day, JD-U chief Sharad Yadav had said that Kumar's resignation was final and he will not go back on the move.
Yadav however refused to comment on the speculation about a possible alliance between the JD-U and Lalu Prasad Yadav's Rashtriya Janata Dal (RJD)
Even as sources said that Kumar was not keen on being re-elected to avoid being called out for playing a political stut, the JD-U is expected to meet again on Monday to carry forward the process and break the impasse.
Nitish Kumar resigned on Saturday following a crushing defeat of his Janata Dal-United at the hands of ally-turned-foe Bharatiya Janata Party (BJP) in the Lok Sabha elections.
The ruling JD-U managed to win just two of the 40 seats in Bihar while the BJP and its allies swept away 31 seats prompting Kumar to resign.
Kumar however did not recommend the dissolution of the state assembly and asserted that a new government could be made with the same assembly.
The 63-year-old former BJP-ally's move had flared speculation about state assembly polls sooner even though they were due by November next year.
Some political analysts said that Kumar was left without a choice but to resign as he was seen losing power, underscored by the fact that six of his ministers who had voiced dissent at parting with the BJP, did not attend a cabinet meeting on Friday - hinting at government collapse.
Kumar had parted ways with the BJP after the right-wing Hindu nationalist party pitched Gujarat Chief Minister Narendra Modi as its Prime Ministerial candidate eight months ago.
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