We show both theoretically and experimentally the temporal cavity soliton formation in a fiber ring laser. The cavity-induced modulation instability can automatically destabilize the CW operation of a fiber ring laser, transferring the CW laser beam into a periodic pulse train. Under strong laser emission, and particularly under the action of the effective gain bandwidth limitation, each pulse of the periodic pulse train could be further shaped into a dissipative soliton. The features of the temporal cavity solitons thus formed are experimentally studied and their similarity and difference to those of the mode-locked fiber lasers are discussed.