لَقِيتُ عَمْرًا رَاكِبَيْنِ
Translation: I met ʿAmr while both of us were riding.
لَقِيتُ: past verb with -tu as its subject.
عَمْرًا: accusative object, marked by fatḥa.
رَاكِبَيْنِ: dual ḥāl, accusative with yāʾ; it describes both the subject and the object.
The dual form means both participants were riding; singular rākiban would describe only one referent.