Generally across HN? Nim's forum? There isn't a single source, I've also found a bunch of Rust/Nim comparison that eventually state something along the lines of Rust is equally safe as Nim[1] and it then gets reiterated on HN.
But I am genuinely interested in where this claim is made, perhaps we need to adjust some documentation or make things more clear - so do point us to it if you find it again.