Is a person possessing two distinct familial relationships (like mother and sister) entitled to inherit based on both connections concurrently?
Chapter on Distant Kindred (Dhawu al-Arham)
Al-Mughni
Book of Inheritance Shares (Farā'id)
Primary text
Inheritance is due based on all existing familial relationships, provided it is possible. This view is held by Ahmad, Umar, Ali, Ibn Mas'ud, Ibn Abbas, and the sound narration from Zayd. It is also the position of Al-Nakh'i, Al-Thawri, Qatadah, Ibn Abi Layla, Abu Hanifa and his school, Yahya bin Adam, Ishaq, Dawud, and one position of Al-Shafi'i. The evidence supporting this is that Allah ordained one-third for the mother and one-half for the sister in the Quran; thus, if the mother is also a sister, she must be given what Allah ordained for her in both verses, equivalent to two distinct persons. Furthermore, these are two relationships, each of which grants inheritance independently, and neither one supersedes or outweighs the other when held separately, so they must be inherited jointly, similar to a husband who is also a paternal cousin, or a maternal cousin who is also a full sibling.
Supporting text
An alternative view, considered correct by some including the sound narration from Zayd, Al-Hasan, Al-Zuhri, Al-Awza'i, Malik, Al-Laith, and Hammad, is that inheritance should be based only on the strongest relationship, which is the one that is never entirely set aside. Another perspective holds that both relationships are set aside because neither grants inheritance independently in Islam when they exist in one person, analogous to when one relationship nullifies the other.