瑜伽論記 1.466

1.466

合成八日者，其第六日能為二損，一分損大海，一分損山地，半入損水，半入損堅，故數成八合但七日。

Regarding 'combining into eight suns,' the sixth sun can bring about two types of damage: one portion damages the great ocean, and one portion damages the mountains and earth. Half falls under damaging water, and half falls under damaging solids; therefore, the count becomes eight, though in combination there are only seven suns.