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.  

أَنَّ رَجُلاً أَتَى النَّبِيَّ ﷺ 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  

Which of your knows what share the Messenger of Allah ﷺ had given to the grandfather from the estate? Ma'qil ibn Yasar said: The Messenger of Allah ﷺ gave him a sixth. He asked: Along with whom? He replied: I do not know. He said: You do not know; what is the use then?  

أَيُّكُمْ يَعْلَمُ مَا وَرَّثَ رَسُولُ اللَّهِ ﷺ الْجَدَّ فَقَالَ مَعْقِلُ بْنُ يَسَارٍ أَنَا وَرَّثَهُ رَسُولُ اللَّهِ ﷺ السُّدُسَ قَالَ مَعَ مَنْ قَالَ لاَ أَدْرِي قَالَ لاَ دَرَيْتَ فَمَا تُغْنِي إِذًا