Where does Kant discuss the Trinity?

Could someone please tell me where in Kant's writings he brings up the trinity? I keep finding this quote on various blogs and articles but nowhere do they reference where it is from.

"The doctrine of the Trinity provides nothing, absolutely nothing, of practical value, even if one claims to understand it; still less when one is convinced that it far surpasses our understanding. It costs the student nothing to accept that we adore three or ten persons in the divinity. … Furthermore, this distinction offers absolutely no guidance for his conduct."

This fits in with my understanding of Kant on the Trinity but I want to read it first hand.