Is a man who concealed his chronic illness when applying for a job obliged to leave his work? Is his concealment considered acceptable, or is he being dishonest in his statements? Is anything required of him for the past period?

The Sharia enjoins truthfulness and forbids lying. Truthfulness guides to righteousness and Paradise, while lying guides to wickedness and Hellfire. Therefore, a believer must be adorned with truthfulness. Tawriya (equivocation/double entendre) is to make the listener understand something other than what is in the speaker's mind. It is not permissible except for a legitimate Sharia interest or to avert harm. It is not permissible for the oppressor, but it is permissible for the oppressed. One should be forthright with one's employer about an illness if it prevents work or affects performance.