«فَفَضَضْتُهَا فِعْلَ الْمُتَلَمِّسِ صَحِيفَةَ الْمُتَلَمِّسِ»
I broke it open as al-Mutalammis once opened his notorious letter.
Al-Mutalammis is associated in Arabic literary tradition with opening a dangerous letter rather than blindly carrying it. The allusion explains why al-Ḥārith inspects Abū Zayd’s sealed note. Faḍaḍtuhā means breaking open something closed or sealed. What he finds is not a legal defence but a mocking poem intended to intensify the governor’s humiliation.