How is the estate distributed among collateral relatives when a spouse (husband or wife) is also an heir?
Chapter on Distant Kindred (Dhawu al-Arham)
Al-Mughni
Book of Inheritance Shares (Farā'id)
Primary text
There is no known disagreement among those who permit inheritance for Dhawu al-Arham that they inherit the remainder after the spouse's fixed share is allocated, without the spouse being veiled (hajb) or causing increase (awl). The primary view, held by our Imam (Ahmad), Abu 'Ubayd, Muhammad ibn al-Hasan, and others, is that the collateral relatives inherit the remainder as they would if they were the sole heirs.
Supporting text
Yahya ibn Adam and Dhirar held that the remaining estate should be divided among the collateral relatives based on the proportion of their shares had they been calculated alongside the spouse, subject to veiling and increase. Then, the spouse's fixed share is allotted fully, and the remainder is divided among the collateral relatives based on their calculated shares. Disagreement arises only when some relatives are connected by a fixed-share heir and others by a residuary heir; if all are connected by fixed shares or all by residuary heirs, there is no dispute.