Srimad-Bhagavatam: Canto 5 - Chapter 1 - Verse 7
Sanskrit:
उपवर्णितं भूमेर्यथासन्निवेशावस्थानमवनेरप्यधस्तात् सप्त भूविवरा एकैकशो योजनायुतान्तरेणायामविस्तारेणोपक्लृप्ता अतलं वितलं सुतलं तलातलं महातलं रसातलं पातालमिति ॥ ७ ॥
ITRANS:
upavarṇitaṁ bhūmer yathā-sanniveśāvasthānam avaner apy adhastāt sapta bhū-vivarā ekaikaśo yojanāyutāntareṇāyāma-vistāreṇopakḷptā atalaṁ vitalaṁ sutalaṁ talātalaṁ mahātalaṁ rasātalaṁ pātālam iti.
Translation:
My dear King, beneath this earth are seven other planets, known as Atala, Vitala, Sutala, Talātala, Mahātala, Rasātala and Pātāla. I have already explained the situation of the planetary systems of earth. The width and length of the seven lower planetary systems are calculated to be exactly the same as those of earth.