جَاءَنِي زَيْدٌ رَاكِبًا
Translation: Zayd came to me while riding.
جَاءَ: past verb, built on fatḥ.
نِ: protective nūn.
ي: first-person attached pronoun in the object position.
زَيْدٌ: nominative subject, marked by ḍamma.
رَاكِبًا: accusative ḥāl, marked by fatḥa; it describes Zayd.
Zayd is the one who came; rākiban specifies his condition while coming.