«فَوَجَدْتُ أَبَا زَيْدٍ قَدْ كَتَبَ عَلَى الْقَتَبِ حِينَ شَمَّرَ لِلْهَرَبِ»
I discovered that Abū Zayd had written on the saddle when he made ready to flee.
Al-qatab is a type of camel saddle, and shammara lil-harab evokes getting ready for flight. The endings of qatab / harab contribute a rhymed-prose effect.
The missed return is no accident. Abū Zayd has fled, but has turned even his escape into a literary performance by leaving behind a poem.