What poem or story does the line big said to small come from where Big and Small are looking at

The line "Big said to Small, / 'Come, we must go and wash' " is from the poem "The Cat and the Mouse" by Robert Louis Stevenson. The poem tells the story of a cat and a mouse who are friends. One day, the cat tells the mouse that they must go and wash. The mouse is scared of the water, but the cat reassures him and they go together to the river. The cat washes the mouse and then dries him off. The mouse is very grateful and tells the cat that he is the best friend a mouse could have.