Yemen has a rich tradition of tribal customary law, variously styled as ‘urf al-qabalī, ḥukm ‘urfī or aḥkām al-man‘, that can be documented back to at least the time of the Yemeni savant al-Ḥasan al-Hamdānī (d. 945 CE). Yemeni tribal law texts from the past three centuries have been studied by several European and Yemeni scholars, including Ettore Rossi, R. B. Serjeant, Paul Dresch, Fāḍil Abū Ghānim and, most recently, Ahmad al-Gabali. There are brief mentions of aspects of customary law in a number of historical sources and travel accounts, but the earliest extant text on Yemeni tribal law is in the mixed archival manuscript compiled for the Rasulid Sultan al-Malik al-Afḍal al-‘Abbās (d. 1377 CE), shortly before his death. This brief text of 62 lines spread over one and a quarter pages is unfortunately not complete and has several lacuna. From the start it discusses five major parts of customary law: protection (dhimām), clientage (jār), escort (rafīq), guest (ḍayf) and marriage (ṣihr). It also mentions the various forms of censure: ‘ayb aswad, ‘ayb aghbar and ‘ayb​ abyaḍ. The text quotes several passages from the Quran and the ḥadīth literature. There is also a reference to the first Zaydī imam, al-Hādī ilā al-Ḥaqq (d. 911 CE) and his grandfather Qāsim b. Ibrāhīm (d. 860 CE). It appears to be authored by a Zaydī scholar, although the name of the author is not indicated in the surviving text. This paper will discuss the contents of the text and its importance for understanding the development of tribal customary law in Yemen.