The Long Āgama Sūtra 30.13

30.13

佛告諸比丘：「如一日月周行四天下，光明所照，如是千世界，千世界中有千日月、千須彌山王、四千天下、四千大天下、四千海水、四千大海、四千龍、四千大龍、四千金翅鳥、四千大金翅鳥、四千惡道、四千大惡道、四千王、四千大王、七千大樹、八千大泥犁、十千大山、千閻羅王、千四天王、千忉利天、千焰摩天、千兜率天、千化自在天、千他化自在天、千梵天，是為小千世界。如一小千世界，爾所小千千世界，是為中千世界。如一中千世界，爾所中千千世界，是為三千大千世界。如是世界周匝成敗，眾生所居名一佛剎。」

The Buddha told the monks, “Just as one sun and moon orbit the four continents and shine their light on them, there are a thousand such worlds. In a thousand worlds, there are a thousand suns and moons, a thousand Sumeru mountain kings, four thousand continents, four thousand great continents, four thousand oceans, four thousand great oceans, four thousand nāgas, four thousand great nāgas, four thousand garuḍas, four thousand great garuḍas, four thousand unpleasant destinies, four thousand great unpleasant destinies, four thousand kings, four thousand great kings, seven thousand great trees, eight thousand great hells, ten thousand great mountains, a thousand King Yamas, a thousand four god kings, a thousand Trāyastriṃśa Heavens, a thousand Yama Heavens, a thousand Tuṣita Heavens, a thousand Nirmāṇarati Heavens, a thousand Paranirmitavaśavartin Heavens, and a thousand Brahma Heavens. This is a small thousand worlds.

“Like one small thousand worlds, a thousand of those small thousand worlds are a medium thousand worlds. Like one medium thousand worlds, a thousand of those medium thousand worlds are a triple-thousand great thousand worlds. Such worlds revolve around as they form and are destroyed. The sentient beings that inhabit them are called a single Buddha realm.”