«فَحِينَ أَحْرَزَ الْعَيْنَ فِي صُرَّتِهِ»
Once he secured the cash in his purse.
Al-ʿayn has several meanings; here it means actual money or ready payment, not an eye. Al-ṣurrah is a small purse or pouch, while aḥraza means to secure or gain possession of something.
The vocabulary changes our understanding of the action: Abū Zayd no longer depends on promises. The money is actually in his possession, setting the stage for his satisfaction and the surprising confession.