This article presents an analysis of Hausa glosses in a nineteenth-century Qur'anic manuscript (C1688) from the library of the Institute of Oriental Manuscripts in St Petersburg, and argues that a systematic study of Arabic manuscripts with Hausa glosses is needed for a re-interpretation of early Hausa writings in Arabic script. The origins of the Hausa written tradition in Arabic script and the evolution of the concept ‘Ajami’ in the nineteenth and twentieth centuries from ‘non-Arabic (language, culture, etc.)’ to ‘a variety of Arabic script adapted to African languages (with additional vowel-signs and diacritics)’ is discussed, and it is suggested that the frequency of the marginal notes ʿajam and ʿajamī used to mark non-Arabic glosses in Arabic manuscripts might depend on the linguistic properties of the manuscripts as well as sub-regional traditions of writing in Sudanic Africa. Hausa glosses in the St Petersburg manuscript – including nouns, adjectives, verbs and verbal constructions – are described in same detail. Special attention is paid to borrowings from Arabic and negative verbal constructions which are not attested in Hausa dialects and modern Standard Hausa. For the first time in Hausa studies, the shift in the meaning of the Hausa word shisshigi (from ‘acting tyrannically’ to ‘meddlesomeness’) is explored. The glosses are compared with the Arabic text of Tafsīr al-Jalālayn and two modern Hausa tafāsīr, those of Abubakar Mahmud Gumi and Nasiru Kabara. It is demonstrated that the Hausa glosses in the St Petersburg Qur'anic MS share a greater affinity with Kabara's tafsīr than with Gumi's translation, and, on this basis, suggested that the translational practices reflected in the St Petersburg manuscript and in Kabara's tafsīr might be linked with the Qādiriyya tradition of Arabic-Hausa ‘translational reading’.