'Abd al-Rahman al-Jaziri — al-Fiqh 'ala al-Madhahib al-Arba'a. Organized comparatively by chapter; the backbone reference. (PDF in this folder: JurisprudenceOfTheFourSunniSchools.pdf)
Ibn Rushd (Averroes) — Bidayat al-Mujtahid wa-Nihayat al-Muqtasid. Source of the sabab al-ikhtilaf (why the schools differ). (PDFs: TheDistinguishedJuristsPrimer Vol 1–2)
al-Mawsu'a al-Fiqhiyya al-Kuwaytiyya — encyclopedic cross-madhhab entries; used for corroboration.
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