Another very good discussion yesterday in these strange times. As I mentioned Parmenides, here is the quote from one of the fragments of the only written piece, a poem, dubbed On Nature:
" Therefore thinking and that by reason of which
95 thought exists are one and the same thing, for thou wilt not find thinking without the being from which it receives its name."
It is really worth reading all the fragments, which you can find here:
https://history.hanover.edu/texts/presoc/parmends.html#truth
A couple of good references about Parmenides and the possible interpretations of his philosophical claims are:
https://www.iep.utm.edu/parmenid/#SSH3bi
https://plato.stanford.edu/entries/parmenides/