Imran ibn Husayn:
A man came to the Prophet (ﷺ) and said: My son has died; what do I receive from his estate? He replied: You receive a sixth. When he turned away he called him and said: You receive another sixth. When he turned away, he called him and said: The other sixth is an allowance (beyond what is due).
Qatadah said: They (the Companions) did not know the heirs with whom he was given (a sixth). Qatadah said: The minimum share given to the grandfather was a sixth.