According to wikipedia, The Famous verse from Vivek Chudamani (विवेकचूडामणि) is:
Brahma satyam jagat mithya, jivo brahmaiva naparah
Translation: Brahman is the only truth, the world is unreal, and there is ultimately no difference between Brahman and individual self
So, Where can I find the verse : Brahma satyam jagat mithya, jivo brahmaiva naparah?
Note: Verse no. 20 of vivek chudamani is not exactly this (though it contains first part of the quoted verse)
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