Found it in Perek Yud Alef (11) as a Zohar in Vayikra.
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The perek quotes a whole bunch of Zohars regarding learning, for example how it is being Mekayim the world, and how anyone who learn Torah every day is Zoche to Olam Haba:
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Shockingly, the Zohars do not limit the Kiyum to those in Kollel, but rather expands the right of Kiyum to all Jews (even MO, OO and Zionists, Chas V’Shalom!!!)
I know, it’s probably a modern-day addition and a forgery :-), so you will have to find me a different source that only Kollel learning (and none other) is mekayem the world.