In many serious engineering and scientific publications including IEEE publications, we see a quote attributed to Nikola Tesla which goes like this
If you want to find the secrets of the universe, think in terms of energy, frequency, and vibration.
However no one gives a reference because this is common quote on social media type posts but no book or publication before the internet era (1990s) ever mentions it. I searched Google Scholar and Google Books with year limited to pre-1999, there is nothing. Is there an authentic reference of this quote? Wiki Quotes also has a reference to a vague website. See for example: https://en.wikiquote.org/wiki/Nikola_Tesla#Disputed