He also composed an epistle on judicial rulings, a single volume, preserved through the transmission of Muḥammad ibn Yūsuf ibn Maṭrūḥ from ʿAbd Allāh ibn ʿAbd al-Jalīl (1).

Another epistle was addressed to Abū Ghassān Muḥammad ibn Muṭarrif (2).

He is further credited with a letter of courtly etiquette sent to the caliph al-Rashīd; its isnād is broken. It was rejected by the judge Ismāʿīl and others, and it contains ḥadiths that are unknown.
I say: this epistle is fabricated.
Judge al-Abharī remarked, “It contains ḥadiths such that, had Mālik heard anyone relate them, he would have disciplined him.” (3)

He also left a fascicle on Qurʾānic exegesis, transmitted by Khālid ibn ʿAbd al-Raḥmān al-Makhzūmī. Qāḍī ʿIyāḍ relates it from Abū Jaʿfar Aḥmad ibn Saʿīd, from Abū ʿAbd Allāh Muḥammad ibn al-Ḥasan al-Muqriʾ, from Muḥammad ibn ʿAlī al-Maṣṣīṣī, from his father, with his full isnād (4).

The book entitled “al-Sirr” (The Secret) is transmitted by Ibn al-Qāsim from Mālik. It was narrated by al-Ḥasan ibn Aḥmad al-ʿUthmānī, from Muḥammad ibn ʿAbd al-ʿAzīz ibn Wazīr al-Jarawī, from al-Ḥārith ibn Miskīn, from him (5).

I add: it is a single fascicle. Abū Muḥammad ibn al-Naḥḥās al-Miṣrī heard it from Muḥammad ibn Bishr al-ʿAkrī. Miqdām ibn Dāwūd al-Ruʿaynī told us: al-Ḥārith ibn Miskīn and Abū Zayd ibn Abī al-Ghimr said, “Ibn al-Qāsim narrated it to us.”