Allah said,

﴿فَإِن كُنَّ نِسَآءً فَوْقَ اثْنَتَيْنِ فَلَهُنَّ ثُلُثَا مَا تَرَكَ﴾

(if only daughters, two or more, their share is two-thirds of the inheritance;) We should mention here that some people said the Ayah only means two daughters, and that `more' is redundant, which is not true. Nothing in the Qur'an is useless or redundant. Had the Ayah been talking about only two women, it would have said, "The share of both of them is two-thirds.'' As for the daughters, two or more, the ruling that they get two-thirds was derived from this Ayah, stating that the two sisters get two-thirds. We also mentioned the Hadith in which the Prophet commanded that two-thirds be the share of the two daughters of Sa`d bin Ar-Rabi`. So this is proven in the Book and the Sunnah.

﴿وَإِن كَانَتْ وَحِدَةً فَلَهَا النِّصْفُ﴾

(if only one, her share is half.) If there are two daughters, then there are texts to prove they share a half. Therefore, two-thirds is the share of the two daughters or sisters, and Allah knows best.