The mushtaraka case — do the full brothers share the uterine siblings’ third?

They share. The third is divided equally between the uterine siblings and the full siblings, and — unusually — a brother takes no more than a sister within it, because all of them are taking as children of the same mother. So a husband, a mother, two uterine brothers and one full brother gives the husband a half, the mother a sixth, and the remaining third split three ways: a ninth each. The reasoning both sources record is that the full brothers are related to the deceased through the same mother as the uterine siblings, and their additional tie through the father cannot be the thing that destroys them: if it does not put them ahead it should at least not put them out. This is the ruling of ‘Uthman and Zayd ibn Thabit, and it is ‘Umar’s second ruling — he had first excluded the full brothers, and changed his mind when they asked him to suppose their father had been a donkey.

Sources: al-Mawsu’a al-Fiqhiyya, “Irth” secs. 147–148 — the configuration (a woman leaving a husband, a mother, two uterine siblings and two full brothers) and the split: the position of ‘Ali, Abu Musa and Ubayy that the full brothers take nothing is “ma dhahaba ilayhi al-Hanafiyya, wa’l-imamu Ahmadu fi’l-asahhi ‘anh”; the position of ‘Uthman and Zayd that the third is shared equally among them all is “ma dhahaba ilayhi Shurayhun, wa’l-Thawriyyu, wa Malikun, wa al-Shafi‘i”; plus the “suppose our father was a donkey” exchange with ‘Umar and his “tilka ‘ala ma qadayna, wa hadhihi ‘ala ma naqdi” (Ministry of Awqaf and Islamic Affairs, Kuwait) · al-Mughni, mas’ala 4831 cont. — “wa saqata al-ikhwatu min al-abi wa’l-umm”; the case is named al-mushrika because some scholars share the uterine siblings’ portion with the full siblings, and al-himariyya from “suppose our father was a donkey — is our mother not one?”; “fa-dhahaba Ahmadu … ila anna … saqata al-ikhwatu min al-abawayni; li-annahum ‘asabatun wa qad tamma al-malu bi’l-furud”, “wa bihi qala … Abu Hanifata wa ashabuh”; against which ‘Umar, ‘Uthman and Zayd shared the third among them all, “wa bihi qala Malikun, wa al-Shafi‘i … wa Ishaq” (Ibn Qudama al-Maqdisi (d. 620 AH)) · al-Mawsu’a al-Fiqhiyya al-Kuwaytiyya, entry “Irth” sec. 147, al-mulaqqabat min masa’il al-mirath — “awwalan: al-mushrika, aw al-himariyya, aw al-hajariyya, aw al-yammiyya”, and the preface that among the named cases “minha ma ittafaqa al-fuqaha’u ‘ala hukmiha, wa minha ma ikhtalafu fih” — this one being of the second kind (Ministry of Awqaf and Islamic Affairs, Kuwait) · al-Mughni, mas’ala 4831 concluded and fasl 4832–4833 — al-‘Anbari’s epigram “al-qiyasu ma qala ‘Aliyyun, wa’l-istihsanu ma qala ‘Umar”, Ibn Qudama’s reply that bare istihsan is no proof, and his remark that al-Shafi‘i adopting it here is surprising given his own “man istahsana fa-qad shara‘a”; plus the variant where the residuaries are CONSANGUINE brothers, who “saqata, qawlan wahidan, wa lam yuwarrithhum ahadun min ahli al-‘ilmi fima ‘alimna” (Ibn Qudama al-Maqdisi (d. 620 AH)) — each school separately named at each locus cited: the Mawsu’a names Malik and al-Shafi’i, and Ibn Qudama names them again in the same order, adding Ishaq.

They take nothing. The full brothers here are residuaries, not holders of a fixed share; the husband’s half, the mother’s sixth and the uterine siblings’ third have already used the estate up, so there is no residue and they drop out — exactly as they would if the fixed shares had been exhausted by two daughters instead. Three reasons are given. Q 4:12 gives the third to the uterine siblings specifically, and the Mawsu’a says the exegetes are agreed on that, so sharing it out contradicts the plain words. The Prophet’s instruction “assign the fixed shares to those entitled to them” is not obeyed by a division that takes part of a fixed share away. And it is agreed on all sides that a single uterine sibling takes a full sixth while a hundred full brothers would take only the residue — so if one may out-take them that far, two may exclude them altogether.

Sources: al-Mawsu’a al-Fiqhiyya, “Irth” secs. 147–148 — the configuration (a woman leaving a husband, a mother, two uterine siblings and two full brothers) and the split: the position of ‘Ali, Abu Musa and Ubayy that the full brothers take nothing is “ma dhahaba ilayhi al-Hanafiyya, wa’l-imamu Ahmadu fi’l-asahhi ‘anh”; the position of ‘Uthman and Zayd that the third is shared equally among them all is “ma dhahaba ilayhi Shurayhun, wa’l-Thawriyyu, wa Malikun, wa al-Shafi‘i”; plus the “suppose our father was a donkey” exchange with ‘Umar and his “tilka ‘ala ma qadayna, wa hadhihi ‘ala ma naqdi” (Ministry of Awqaf and Islamic Affairs, Kuwait) · al-Mughni, mas’ala 4831 cont. — “wa saqata al-ikhwatu min al-abi wa’l-umm”; the case is named al-mushrika because some scholars share the uterine siblings’ portion with the full siblings, and al-himariyya from “suppose our father was a donkey — is our mother not one?”; “fa-dhahaba Ahmadu … ila anna … saqata al-ikhwatu min al-abawayni; li-annahum ‘asabatun wa qad tamma al-malu bi’l-furud”, “wa bihi qala … Abu Hanifata wa ashabuh”; against which ‘Umar, ‘Uthman and Zayd shared the third among them all, “wa bihi qala Malikun, wa al-Shafi‘i … wa Ishaq” (Ibn Qudama al-Maqdisi (d. 620 AH)) · al-Mawsu’a al-Fiqhiyya, “Irth” sec. 150 — the arguments AGAINST sharing: Q 4:12, “idh la khilafa fi anna al-murada bi’l-ayati awladu al-ummi ‘ala al-khusus, kama ajma‘a ‘ala dhalika al-mufassirun”; the hadith “alhiqu al-fara’ida bi-ahliha”; and the consensus that one uterine sibling takes a sixth while any number of full brothers take only the residue (Ministry of Awqaf and Islamic Affairs, Kuwait) · Ibn Qudama, al-Mughni, mas’ala 4831 — al-Khiraqi’s text: “wa idha kana zawjun wa ummun wa ikhwatun min ummin wa ikhwatun li-abin wa umm, fa-li’l-zawji al-nisfu, wa li’l-ummi al-sudusu, wa li’l-ikhwati min al-ummi al-thuluth” (Ibn Qudama al-Maqdisi (d. 620 AH)) · al-Mughni, mas’ala 4831 concluded and fasl 4832–4833 — al-‘Anbari’s epigram “al-qiyasu ma qala ‘Aliyyun, wa’l-istihsanu ma qala ‘Umar”, Ibn Qudama’s reply that bare istihsan is no proof, and his remark that al-Shafi‘i adopting it here is surprising given his own “man istahsana fa-qad shara‘a”; plus the variant where the residuaries are CONSANGUINE brothers, who “saqata, qawlan wahidan, wa lam yuwarrithhum ahadun min ahli al-‘ilmi fima ‘alimna” (Ibn Qudama al-Maqdisi (d. 620 AH)) — the Hanbali position is the school’s own text (al-Khiraqi’s matn, on which al-Mughni is a commentary) and the Mawsu’a records it as Ahmad’s position fi’l-asahhi ‘anh, on the sounder of the reports from him — not a settled single narration; the Hanafi position is attributed by Ibn Qudama to “Abu Hanifa and his companions” and by the Mawsu’a to al-Hanafiyya as a school.