Scabious was mentioned when Holly was telling his story to the rabbits of Watership down and explained that Scabious was killed when the men shot him, but he mentioned that he was so confused by the gas that he didn't feel the pain. Pipkin was tormented by the thought of Scabious being killed for nothing.
It can also be referring to a different Scabious son of Clover. He and his siblings were being trained by Bigwig at the end of the book. He was training them how to get around a cat but Scabious wanted to hear some stories instead.