[1] Sometime in the last quarter of the ninth century, he compiled the first nomocanon (collection of canon law) in the history of the Church of the East.
Only fragments of the original Syriac survive, but the work can be largely reconstructed because of its extensive quotation and citation in the Arabic collection Fiqh al-Naṣrāniyya of Ibn al-Ṭayyib (11th century) and the Syriac Nomokanon of ʿAbdishoʿ bar Brikha (14th century).
[2] Hubert Kaufhold performed the work of reconstruction, publishing it with a German translation in Die Rechtssammlung des Gabriel von Baṣra (1976).
[3] Gabriel's nomocanon is structured in the form of questions and answers, although this is a purely formal device for introducing quotations from his sources.
[2] He also used the legal writings of East Syriac scholars like Ishoʿbokht, Shemʿon of Rev Ardashir and ʿAbdishoʿ bar Bahrīz.