成唯識論演祕 4.123

4.123

舉喻釋成。既汝行支由懸隔故，不能感果，應同外法不得名為異熟之因。

This adduces an analogy to explain and establish the point. Since your branch of formations, due to being distantly separated, cannot induce a fruit, it should, like external things, be unable to be called a cause of maturation.