Kumar did not respond to repeated queries of reporters on the issue while leaving the Gandhi Sangrahalay after attending a function.
"Jyada bolne par gala kharab ho jata hai (speaking more leads to a sore throat)," was all that Kumar said.
Deputy chief minister Tejaswi Yadav also did not comment on the issue.
Tejaswi, the younger son of Lalu Prasad, has been targeted by Sushil Modi with a series of allegations of dubious land deals.
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"He is making allegations as part of some political agenda... He should approach the competent authority with his allegations, instead of making political statements everyday," Choudhary told reporters.
"Why should we work on an agenda set by Sushil Modi? we have our own agenda to work for the people of Bihar," Choudhary, the state Education minister, said.
He dismissed any cracks in the grand alliance in the state, which he said is standing rock solid.
Sushil Modi has been making allegations of dubious land deals by Lalu Prasad's family members and has demanded that Kumar sack Lalu's two sons from the ministry.
"If RJD spokesman Manoj Jha produces any paper with regard to allegations about me owning property in Rajendra Nagar in Patna, Sohna in Haryana, moving around in BMW cars in Bengaluru and Mumbai and fake degree of my wife, then I will register the entire property in the name of Lalu Prasad or file a defamation suit against Jha," Sushil Modi said in a statement.