In general, I'd be very cautious of accepting anything Hitchens says without backing it up--he's kind of the posterchild for New Atheist bad history/bad pre-history. From your description it sounds like something Matteo Ricci or one of his Jesuit brethren would have dealt with--they interacted with the political elite far more frequently than the Protestants did. Unfortunately, that description is so vague that I can't narrow it down any further without at least a dynasty name, and I wrote an MA thesis that dealt heavily with Western missionaries to China. Perhaps u/keyilan can help out?

I've seen a lot of skepticism in the comments, and I am unfamiliar with Hitchens so cannot comment. Initially I intended to revise my old comment, but I'll create a new one because I think the source is important enough. I managed to find the source that I think is being talked about, and will relay it here.

To fully respond to the question, I don't think this can be considered a singular event, since this was written, and seems a response to Catholicism and the missionaries in general, rather than a direct criticism.

The source seems to be from Yi Ik titled "Matteo Ricci's Catechism," (p. 124-127) from the Sources of Korean Tradition, vol. 2 by Peter H. Lee and Wm. Theodore de Bary, and edited by Yongho Choe. According to de Bary, Yi Ik was a scholar who read and critiqued the philosophical works of Christians in China. He was apparently born in 1681, so this would put him in the Joseon Dynasty, to respond to one of the other comments, and this text would probably fall in the early 1700s, well after the actual arrival of missionaries to China.

I'll excerpt the particularly relevant part:

"If the Lord of Heaven truly felt compassion for mankind and descended to this earth in human form, walking and talking among men like any other man, then, since int he million places on this earth there are an infinite number of people deserving of his compassion, he should have admonished them all one by one. But how could the Lord of Heaven, in the form of just one man, do all that? Those living outside of Europe, those who have never heard of these European teachings, have seen no signs of his having visited them. What is so special about Europeans that he has so favored them with his visits? And what about all these miraculous signs of the Lord's presence that Europe claims? How do we know they are not simply the tricks of evil spirits?" (p. 126)

I am pretty sure this is the source in question because of this paragraph. Yi essentially argues that if those outside of Europe were never exposed to Christianity, then God cannot truly be compassionate in the way that the missionaries describe. He challenges their viewpoint on it. He focuses more on the idea of heaven and hell in opposition to reincarnation, which the missionaries saw as a flaw of Buddhism (they attribute the concept to "evil spirits," which he reverses on them).

You can find the full text in the source I mentioned. It's not very long, and is a pretty brief rebuttal to some major arguments of the missionaries, albeit over a century later.

Edit: added page numbers. I wish I could relay the entire piece as it's actually pretty interesting, so if anyone is interested I'd recommend going to the library (or I could upload the pictures I took in between classes).

I'd agree with approaching the anecdote with caution. It depends on which point of Christianity's introduction to China we're talking about (there were multiple).

Nestorian Christianity came to China during the Tang dynasty and was well-received by the emperor.

In 638, the emperor Taizong issued this edict:

"The way does not have a common name and the sacred does not have a common form. Aluoben, the man of great virtue from the DaQin empire, came from a far land...his message is mysterious and wonderful beyond our understanding. The message is lucid and clear; the teachings will benefit all; and they shall be practiced throughout the land." (from Daniel H. Bays' [A New History of Christianity in China] ( http://www.worldcat.org/oclc/707263763), page 9).

There's also the problem of assuming that "religion" has always been understood as an either/or concept. As in, you belonged to one religion, and no other, and that only one religion could be true. Most scholars of religion agree that the idea of "conversion" to a single religion was something that was introduced by Christianity (See A.D. Nock's Conversion) and was hard to grasp by many of the cultures on the receiving end of Christian missionary work (David Chidester's Savage Systems comes to mind.

That being said, Daniel Bays mentions a Buddhist-Christian "debate" (his quotes) in May of 1254 involving the Franciscan missionary Willem van Rubroek (William of Rubruck), but Bays doesn't give any other details, nor does he provide a source. But perhaps this is the conversation you're thinking of?