Prison officials said he was admitted to the ICU of the hospital two-three days ago.
They have been arrested for aiding Shahabuddin in writing the law exam.
The court said that after casting his vote, he would be immediately taken back to Siwan jail.
A proclamation and property attachment notice was on Monday pasted at the house of Laddan Mian, a close associate of jailed ex-Rashtriya Janata Dal MP Mohammad Shahabuddin, in connection with the murder of a journalist in Siwan earlier this month.
He was not comfortable with the bahubali politician's presence in Siwan after his release.
Ex-RJD MP has been charged with murder and criminal conspiracy in the killing of journalist Rajdeo Ranjan.
The accused say a close aide of former RJD MP Shahabuddin gave them a supari to kill Ranjan.
Nitish Kumar had a week's time to prove his majority, but Laloo Yadav made full use of Siwan don Mohammad Shahabuddin. A revealing excerpt from Rajesh Singh's Baahubalis Of Indian Politics: From Bullet To Ballot.