The RJD supremo, who has been in jail for more than two months following his conviction in fodder scam cases, made the attack on Twitter, which is managed by people close to Prasad.
He asked Kumar why he did not put enough pressure on Prime Minister Narendra Modi to offer special status to Bihar.
Prasad's comments came in the backdrop of Telugu Desam Party ministers resigning from the Union council of ministers over the demand for special status to Andhra Pradesh.
He accused Kumar of having surrendered Bihar's interest for personal gains - an oblique reference to the chief minister's exit from the Grand Alliance and forming a new government in the state with the BJP.
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In another tweet, the former Bihar chief minister asked, "Why is Bihar not getting special status despite the NDA being in power both at the Centre and in the state? Does Nitish not want special status or is the BJP opposed to it?"
The RJD chief also sought to know how much of the Rs 1.65 lakh crore announced by Modi as special package has been given to the state.
"Actually, the state has not got even a penny. Admit it, if you have the guts. How long will you keep hoodwinking the people," the RJD supremo added.