He said he can't reveal the name for he fears for the person's life. Earlier this month, Bhushan had submitted in court the details of cars and people at the CBI chief's house.
The court had asked Bhushan to reveal the name of the whistle-blower.
Centre for Public litigation or CPIL run by the senior lawyer said in a statement that they got the information "from a confidential and reliable source whose identity needs to be protected."
Bhushan has accused Ranit Sinha of compromising probes into some huge financial scams. Sinha has, hower, refuted the allegations.