I’ve a grand memory for forgetting, David.

Robert Louis Stevenson (1850–1894) Scottish essayist, novelist, poet

Novel (1886), Kidnapped, ch. 18 “I Talk with Alan in the Wood of Lettermore” [Alan]
    (Source)

Suggesting he will soon "forget" the name of the murderer of a Campbell.

This chapter was originally published in Young Folks Paper, Vol. 28, No. 812 (1886-06-19)