I recently played in an adventure with a new group, and after killing a dragon, the rest of the group started talking about butchering the dragon, harvesting its scales, blood, eyes, fangs, etc., specifically so we could sell them for money. I was shocked that we were talking about breaking down a sentient creature for parts, but both other players and the DM seemed to feel like this was a normal thing to do. In further research, every group of D&D players I've asked has told me this is something they've seen in their games, or heard about as a normal thing to happen. Somehow, in 20 years of playing D&D, this idea has entirely missed me.
I've checked through a few questions here (including a 5e one here) that ask about the mechanics for harvesting dragon parts, and generally what I've seen is that in 5e and 4e, there were no mechanics for this, and in 3.5 the only source about this was the Draconomicon. The one exception being the rules in 3.0/3.5 about how to harvest dragon hide, specifically, for Dragonhide Armor.
It's strange to me that something with no apparent rules justification is treated as such a normal thing, so I'm trying to figure out where this idea comes from. Specifically, I'm looking for the first time in D&D that there were rules that specifically showed what dragon parts were harvestable, how much they could be sold for, or any other indication that harvesting dragons parts for money was a thing supported by the rules. Magic item creation rules that gave benefits for using dragon parts other than hide would also work. If there are no such rules in any D&D edition, then showing a non-rules source supporting dragon harvesting in D&D (maybe dialog in an adventure or something? flavor text somewhere?) would likewise answer my question.
Where exactly did the idea that you could sell dragon parts come from?