He was referring to the attachment of a piece of land allegedly belonging to family members of the RJD chief by the ED in Patna yesterday.
A mall was reportedly supposed to be constructed on the plot said to be worth about Rs 45 crore.
"Upon attachment of 3 acres of land in Patna by the ED, Lalu Prasad and (his son) Tejashwi (Yadav) have started asking why a charge sheet has not been filed months after the lodging of an FIR in the land-for-hotels scam.
"Actually, the agencies have such strong evidence against them that they will not only face charge sheet but also be sent to jail and awarded punishment", Mr Modi said in a statement here.
Tejashwi Yadav, who is Mr Prasad's younger son, had termed the action by the ED as "political vendetta" and questioned why the agencies had failed to file a charge sheet despite the lapse of five months after the lodging of the FIR.
"If Tejashwi had an answer, he would not have lost his chair," Mr Modi said, in an obvious dig at the RJD losing power in the state earlier this year.
Tejashwi Yadav had become the deputy chief minister after the Grand Alliance comprising Nitish Kumar's JD(U), the RJD and the Congress registered an impressive victory in the 2015 Assembly polls.
However, the coalition came under strain after Tejashwi Yadav's name cropped up in the corruption scandal in the wake of land-for-hotels case.
Mr Kumar and his party JD(U) had asked him at that time to come clean on the issue by giving a public explanation but the RJD turned down the suggestion. Finally, Mr Kumar resigned from the chief minister's post and formed a new coalition government with the BJP.