Which book features 'Hazel', 'Fiver' and 'Bigwig'?

Watership Down is a fantasy adventure novel by English author Richard Adams, published by Rex Collings Ltd of London in 1972. Set in southern England, the story features a small group of rabbits. Although they live in their natural environment, they are anthropomorphised, possessing their own culture, language, proverbs, poetry, and mythology. Evoking epic themes, the novel follows the rabbits as they escape the destruction of their warren and seek a place to establish a new home, encountering perils and temptations along the way.

Three of the characters are:

Hazel: The protagonist, Fiver's brother; he leads the rabbits from Sandleford and eventually becomes Chief Rabbit. Though Hazel is not particularly large or powerful, he is loyal, brave, and a quick thinker.

Fiver: A runt rabbit whose name literally means "Little Thousand" and Hazel's younger brother. As a seer, he has visions and very strong instincts. Fiver is one of the most intelligent rabbits in the group.

Bigwig: An ex-Owsla officer, and the largest and bravest rabbit of the group. His name in Lapine is Thlayli, which literally means "Fur-head" and refers to the shock of fur on the back of his head.