“Knowledge is power; knowledge shared is power lost.”
This has been attributed to Crowley on the internet, but without citation. No incidents of it in Crowley's works have as yet been located.
This was quoted as an "occult tradition" in Fundamentals of Experimental Psychology (1976) by Charles Lawrence Sheridan, p. 17, but without any reference to Crowley.
Disputed
Variant: Knowledge is power and knowledge shared is power lost.
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Aleister Crowley 142
poet, mountaineer, occultist 1875–1947Related quotes

Source: Kritik der zynischen Vernunft [Critique of Cynical Reason] (1983), p. 77

This is the sentence that dug the grave of philosophy in the nineteenth century. … This sentence brings to an end the tradition of a knowledge that, as its name indicates, was an erotic theory—the love of truth and the truth through love (Liebeswahrheit). … Those who utter the sentence reveal the truth. However, with the utterance they want to achieve more than truth: They want to intervene in the game of power.
Source: Kritik der zynischen Vernunft [Critique of Cynical Reason] (1983), p. xxvii
Source: Leviathan

“There is no knowledge that is not power.”
Old Age
1870s, Society and Solitude (1870)
Source: Think (1999), Chapter Four, The Self, p. 146

“Knowledge itself is power.”
Nam et ipsa scientia potestas est.
Meditationes Sacræ [Sacred Meditations] (1597) "De Hæresibus" [Of Heresies]
Variants:
Scientia Ipsa Potentia Est.
Scientia potentia est.
Knowledge is power.
Scientia potestas est.
Scientia est potentia.
Source: Meditations Sacrae and Human Philosophy Meditations Sacrae and Human Philosophy