The word(s) "two-thirds" appears 2 time(s) in 2 verse(s) in Quran in Mohsin Khan translation.

(1) Allah commands you as regards your children's (inheritance): to the male, a portion equal to that of two females; if (there are) only daughters, two or more, their share is two-thirds of the inheritance; if only one, her share is a half. For parents, a sixth share of inheritance to each if the deceased left children; if no children, and the parents are the (only) heirs, the mother has a third; if the deceased left brothers (or sisters), the mother has a sixth. (The distribution in all cases is) after the payment of legacies he may have bequeathed or debts. You know not which of them, whether your parents or your children, are nearest to you in benefit; (these fixed shares) are ordained by Allah. And Allah is Ever All-Knower, All-Wise.

(2) They ask you for a legal verdict. Say: "Allah directs (thus) about Al-Kalalah (those who leave neither descendants nor ascendants as heirs). If it is a man that dies leaving a sister, but no child, she shall have half the inheritance. If (such a deceased was) a woman, who left no child, her brother takes her inheritance. If there are two sisters, they shall have two-thirds of the inheritance; if there are brothers and sisters, the male will have twice the share of the female. (Thus) does Allah make clear to you (His Law) lest you go astray. And Allah is the All-Knower of everything."