حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّهُ بَلَغَهُ أَنَّ مُعَاوِيَةَ بْنَ أَبِي سُفْيَانَ، كَتَبَ إِلَى زَيْدِ بْنِ ثَابِتٍ يَسْأَلُهُ عَنِ الْجَدِّ، فَكَتَبَ إِلَيْهِ زَيْدُ بْنُ ثَابِتٍ إِنَّكَ كَتَبْتَ إِلَىَّ تَسْأَلُنِي عَنِ الْجَدِّ، وَاللَّهُ، أَعْلَمُ وَذَلِكَ مِمَّا لَمْ يَكُنْ يَقْضِي فِيهِ إِلاَّ الأُمَرَاءُ - يَعْنِي الْخُلَفَاءَ - وَقَدْ حَضَرْتُ الْخَلِيفَتَيْنِ قَبْلَكَ يُعْطِيَانِهِ النِّصْفَ مَعَ الأَخِ الْوَاحِدِ وَالثُّلُثَ مَعَ الاِثْنَيْنِ فَإِنْ كَثُرَتِ الإِخْوَةُ لَمْ يُنَقِّصُوهُ مِنَ الثُّلُثِ ‏.‏

Yahya related to me from Malik from Yahya ibn Said that he hadheard that Muawiya ibn Abi Sufyan wrote to Zayd ibn Thabit asking himabout the grandfather. Zayd ibn Thabit wrote to him, "You have writtento me asking me about the grandfather. Allah knows best. That is partof what is only determined by the amirs, i.e. the khalifs. I waspresent with two khalifs before you who gave the grandfather a halfwith one sibling, and a third with two. If there were more siblings,they did not decrease his third." Translation Not Available

Book reference: Muwatta Imam Malik Book 27 Hadith 1077
Web reference: Muwatta Imam Malik Book 27 Hadith 1