The word(s) "eighth" appears 2 time(s) in 2 verse(s) in Quran in Saheeh International translation.

(1) And for you is half of what your wives leave if they have no child. But if they have a child, for you is one fourth of what they leave, after any bequest they [may have] made or debt. And for the wives is one fourth if you leave no child. But if you leave a child, then for them is an eighth of what you leave, after any bequest you [may have] made or debt. And if a man or woman leaves neither ascendants nor descendants but has a brother or a sister, then for each one of them is a sixth. But if they are more than two, they share a third, after any bequest which was made or debt, as long as there is no detriment [caused]. [This is] an ordinance from Allah, and Allah is Knowing and Forbearing.

(2) They will say there were three, the fourth of them being their dog; and they will say there were five, the sixth of them being their dog - guessing at the unseen; and they will say there were seven, and the eighth of them was their dog. Say, [O Muhammad], "My Lord is most knowing of their number. None knows them except a few. So do not argue about them except with an obvious argument and do not inquire about them among [the speculators] from anyone."