Wahb bin Kaysan relates that Abdullah bin Utbah, whom Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with them both) had appointed as governor over Iraq, wrote to him asking about (the inheritance of) the grandfather. So he wrote back in reply: The one (Abu Bakr, may Allah be pleased with him) about whom the Messenger of Allah (peace and blessings be upon him) said: "If I were to take a khalil (intimate friend), I would have taken him as a khalil," placed the grandfather in the position of the father, by which he becomes entitled to the inheritance.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13917