Narrated 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.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، أَخْبَرَنَا هَمَّامٌ، عَنْ قَتَادَةَ، عَنِ الْحَسَنِ، عَنْ عِمْرَانَ بْنِ حُصَيْنٍ، أَنَّ رَجُلاً، أَتَى النَّبِيَّ صلى الله عليه وسلم فَقَالَ إِنَّ ابْنَ ابْنِي مَاتَ فَمَا لِي مِنْ مِيرَاثِهِ فَقَالَ " لَكَ السُّدُسُ " . فَلَمَّا أَدْبَرَ دَعَاهُ فَقَالَ " لَكَ سُدُسٌ آخَرُ " . فَلَمَّا أَدْبَرَ دَعَاهُ فَقَالَ " إِنَّ السُّدُسَ الآخَرَ طُعْمَةٌ " . قَالَ قَتَادَةُ فَلاَ يَدْرُونَ مَعَ أَىِّ شَىْءٍ وَرَّثَهُ . قَالَ قَتَادَةُ أَقَلُّ شَىْءٍ وَرِثَ الْجَدُّ السُّدُسَ .
sunnah.com