The Hound of Tindalos

"There is curved time, and angular time. The beings that exist in angular time cannot enter curved time. It is very strange." (...) "They scented me in time." he moaned. "I went too far."
"What were they like?" I said (...).
He leaned forward and gripped my arm. He was shivering horribly. "No words in our language can describe them!"
(...)
"They are horrors of the soul, and yet"—he hid his face in his hands and groaned—"they are real, Frank. I saw them for a ghastly moment. For a moment I stood on the other side. I stood on the pale gray shores beyond time and space. In an awful light that was not light, in a silence that shrieked, I saw them.

"All the evil in the universe was concentrated in their lean, hungry bodies. Or had they bodies? I saw them only for a moment; I cannot be certain. But I heard them breathe. Indescribably for a moment I felt their breath upon my face. They turned toward me and I fled screaming. In a single moment I fled screaming through time. I fled down quintillions of years."

(...)
"They are lean and athirst!" he shrieked. "The Hounds of Tindalos!"

The Hounds of Tindalos (1929)
by Frank Belknap Long

Inspired by the Xenomorph design too