Amos & Boris / William Steig,

Amos the mouse and Boris the whale: a devoted pair of friends with nothing at all in common, except good hearts and a willingness to help their fellow mammal. They meet after Amos sets out to sail the sea and finds himself in extreme need of rescue. And there will come a day, long after Boris has gone back to a life at sea and Amos has gone back to life on dry land, when the tiny mouse must find a way to rescue the great whale.

Amos & Boris is a 1971 New York Times Book Review Best Illustrated Book of the Year, Notable Children's Book of the Year, and Outstanding Book of the Year.