https://www.npr.org/templates/story/story.php?storyId=129068...
I wonder. The most charitable, or most people that are charitable? According to this[1] (which references a paywalled report), middle-class Americans account for nearly two-thirds of charitable giving. That doesn't necessarily mean the rest is from upper class giving, but I think it's a fairly safe assumption (especially given some of the other points in the article). And if the rich are giving, it might be less of an empathy, and more of a sympathy (or even guilt).
Then again, perhaps you meant the most charitable as in giving the largest percentage of their income. Or maybe of their disposable income, in which case, maybe the poor would actually be the most charitable in some areas.
In any case, I think charitable giving is actually a fairly complex topic that might not be accurately summed up as easily as your comment implies.
1: https://www.philanthropy.com/article/America-s-Generosity-Di...