In the chapter "Ideals of Life" of My Country and My People, Lin Yutang writes (emphasis mine),
The Confucian conception of man's place in nature is that "Heaven, earth and man" are regarded as "the three geniuses of the universe". This is a distinction somewhat corresponding to the Babbittian threefold distinction of supernaturalism, humanism and naturalism.
The rest of the paragraph goes on discussing the Confucian view on man's place in the universe; Irving Babbitt is not mentioned anywhere else in the book.
It is not immediately obvious from Wikipedia's article on Irving Babbitt whether this distinction was expressed in a specific publication. The article Irving Babbitt and Lin Yutang (2014), which discusses Irving Babbitt's influence on Lin Yutang, is not helpful either. The article Philosophy 312: Oriental Philosophy Naturalism, Supernaturalism, and Humanism on Lander University's Eastern Philosophy website discusses naturalism, supernaturalism and humanism without mentioning Babbitt. So what exactly was Lin Yutang's source?