佛祖統紀 30.55

30.55

大三災者。一大劫終必一火災起（如前賢劫成住壞空八十小劫。為一大劫）如是經七大劫七火災。凡七壞初禪。復經一大劫。有一水災起。壞至二禪。如是七七火災。相間七水災。復經七火災。凡五十六番火壞初禪。七番水壞二禪。復經一大劫。有一風災起。總之為六十四大劫。為大三災始終之相（依俱舍論出義）。

As for the great three disasters: at the end of each great kalpa, a disaster of fire must arise (as described above, the eighty small kalpas of formation, duration, destruction, and voidness of the Fortunate Kalpa constitute one great kalpa). After seven great kalpas and seven fire disasters pass like this, having destroyed the First Dhyāna seven times in all, another great kalpa passes and a water disaster arises, destroying up to the Second Dhyāna. Thus, seven times seven fire disasters alternate with seven water disasters; then after another seven fire disasters, in all fifty-six rounds of fire destroy the First Dhyāna, and seven rounds of water destroy the Second Dhyāna. When yet another great kalpa passes, a wind disaster arises. In total, this makes sixty-four great kalpas, which constitutes the full sequence from beginning to end of the three great disasters (the meaning is derived from the Abhidharmakośa-bhāṣya).