Musannaf Ibn Abi Shayba 26:259

Abu Mu'awiyah narrated to us, from al-A'mash, from Ibn Sirin, who said: 'Abdullah used to grant inheritance to grandmothers, even if they were ten [in number]. And he would say: "It is merely a share that the Messenger of Allah, may Allah bless him and grant him peace, fed them."