That’s metaphysics, my dear fellow. It’s forbidden by my doctors, my stomach won’t take it.

Boris Pasternak (1890-1960) Russian poet, novelist, and literary translator
Doctor Zhivago [До́ктор Жива́го], Part 1, ch. 1 “The Five O’Clock Express,” sec. 5 [Ivan Ivanovich] (1955) [tr. Hayward & Harari (1958), US ed.]
    (Source)

After a long argument by Voskoboinikov to avowed atheist Ivanovich as to the necessity of Christianity and the Gospels.

Alternate translations:

That’s metaphysics, my dear fellow. It's forbidden me by my doctors, my stomach won’t take it.
[tr. Hayward & Harari (1958), UK ed.]

Metaphysics, old boy. It's forbidden me by my doctors; my stomach can't digest it.
[tr. Pevear & Volokhonsky (2010)]