Shiva Purana
अष्टाविंशतिसंख्याभिः क्षित्यधस्सप्तकोटयः॥ सप्तमस्य तलस्यांते घोरे तमसि संस्थितः॥ १७॥
At the end of the seventh nether-world Tala, there are twenty-eight Narakakotis situated in terrible darkness.
english translation
aSTAviMzatisaMkhyAbhiH kSityadhassaptakoTayaH॥ saptamasya talasyAMte ghore tamasi saMsthitaH॥ 17॥
hk transliteration by Sanscript