Pretty much any time it describes Grendel, the book describes him ad "God-cursed" or "from Cane's clan". God cast out Cane from the Garden of Eden because Cane committed the first murder on earth. I know that it talks about Grendel a lot in one of the first few pages, so that's where I would look for a specific passage. Text also alludes to the creation of the world in the same passage. I don't have my book with me rn or else I'd give you line numbers.
