Musnad Ahmad 790:101

Yazid narrated to us, Hammam—meaning Ibn Yahya—informed us, from Qatadah, from al-Hasan, from ‘Imran ibn Husayn, that a man came to the Prophet, peace and blessings of Allah be upon him, and said: "My son’s son has died, so what do I have of his inheritance?" He said: "You have the sixth." When he turned away, he called him and said: "You have another sixth." When he turned away, he called him and said: "The other sixth is a gift."