Doesn't exist.
I don't know if this was ever common knowledge, but it's certainly not a new idea. Free software, per the Free Software Foundation, is only free if people are free to redistribute it commercially without having to pay the author. In a sense, every time you build a Drupal site for someone else for a fee, you are charging to distribute free software to them that was authored by other people while providing additional services to tailor it to their needs.
If I had to guess, the more mainstream open source as a development methodology became, the more people adopted it without understanding or appreciating its philosophical origins. Open source as a growth strategy became inevitable while simultaneously kicking against the goads of the four essential freedoms of the movement that birthed it, even though these freedoms are what enabled multi-billion dollar ecosystems like Drupal's to grow.
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