Musnad Ahmad 26:869

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Abu Qays, from Huzayl ibn Shurahbil, who said: A man asked Abu Musa al-Ash'ari about a woman who left behind her daughter, her son's daughter, and her sister. He said: "The daughter gets half, and the sister gets half." And he said: "Go to Ibn Mas'ud, for he will agree with me." He said: So they went to Ibn Mas'ud and informed him of Abu Musa's statement. He said: "I would have gone astray then, and I would not be among the guided. I will judge regarding it with the judgment of the Messenger of Allah (peace and blessings of Allah be upon him)." Shu'bah said: "I found this wording written: 'I will judge regarding it with the judgment of the Messenger of Allah (peace and blessings of Allah be upon him): The daughter gets half, the son's daughter gets one-sixth, to complete the two-thirds, and whatever remains is for the sister.'" So they went to Abu Musa and informed him of Ibn Mas'ud's statement. Abu Musa said: "Do not ask me about anything as long as this scholar is among you."