The word(s) "thirds" appears 3 time(s) in 3 verse(s) in Quran in Saheeh International translation.

(1) Allah instructs you concerning your children: for the male, what is equal to the share of two females. But if there are [only] daughters, two or more, for them is two thirds of one's estate. And if there is only one, for her is half. And for one's parents, to each one of them is a sixth of his estate if he left children. But if he had no children and the parents [alone] inherit from him, then for his mother is one third. And if he had brothers [or sisters], for his mother is a sixth, after any bequest he [may have] made or debt. Your parents or your children - you know not which of them are nearest to you in benefit. [These shares are] an obligation [imposed] by Allah. Indeed, Allah is ever Knowing and Wise.

(2) They request from you a [legal] ruling. Say, "Allah gives you a ruling concerning one having neither descendants nor ascendants [as heirs]." If a man dies, leaving no child but [only] a sister, she will have half of what he left. And he inherits from her if she [dies and] has no child. But if there are two sisters [or more], they will have two-thirds of what he left. If there are both brothers and sisters, the male will have the share of two females. Allah makes clear to you [His law], lest you go astray. And Allah is Knowing of all things.

(3) Indeed, your Lord knows, [O Muhammad], that you stand [in prayer] almost two thirds of the night or half of it or a third of it, and [so do] a group of those with you. And Allah determines [the extent of] the night and the day. He has known that you [Muslims] will not be able to do it and has turned to you in forgiveness, so recite what is easy [for you] of the Qur'an. He has known that there will be among you those who are ill and others traveling throughout the land seeking [something] of the bounty of Allah and others fighting for the cause of Allah. So recite what is easy from it and establish prayer and give zakah and loan Allah a goodly loan. And whatever good you put forward for yourselves - you will find it with Allah. It is better and greater in reward. And seek forgiveness of Allah. Indeed, Allah is Forgiving and Merciful.