Sayyidina Imran ibn Husayn reported that a man came to the Prophet and said, ‘My son has died. So, what is there for me in inheritance?” He said, “For you is one-sixth.: As he was departing, he called him (again) and said, “you have an additional one-sixth.’ Again, as he was going, he called him to him and said, “The additional one-sixth for was through asbah (not mafrudah).
[Abu Dawud 2896]
--------------------------------------------------------------------------------