佛祖統紀 30.50

30.50

空二十小劫（減增）。自初禪梵世已下世界空虛。猶如墨穴。無晝夜日月。唯有大冥。如是二十增減之久。名為空劫（俱舍）。

Empty: twenty small kalpas (decreases and increases). From the Brahmā world of the First Dhyāna downward, the worlds are empty and void, just like a pit of ink. There is neither day nor night, sun nor moon, but only vast darkness. Lasting for twenty increases and decreases like this, it is called the empty kalpa (Kośa).