What is the ruling on money received by a claimant, knowing that he resorted to deception to obtain it by feigning a non-existent nervous illness, while his injury was in the knee?

You erred by falsely claiming illness to qualify for a pension. Lying is forbidden, and you must repent. If the state system provides pensions for those afflicted, and your affliction meets the criteria, then you may take it. However, if the pension is from a private, non-governmental employer, it is not permissible to take it, unless the employer is responsible for the affliction.