Sahih al-Bukhari 2747

Narrated Ibn `Abbas: (During the early days of Islam), the inheritance used to be given to one's offspring and legacy used tobe bequeathed to the parents, then Allah cancelled what He wished from that order and decreed thatthe male should be given the equivalent of the portion of two females, and for the parents one-sixthfor each of them, and for one's wife one-eighth (if the deceased has children) and one-fourth (if he hasno children), for one's husband one-half (if the deceased has no children) and one-fourth (if she haschildren).