مَرَرْتُ بِزَيْدٍ
Translation: I passed by Zayd.
مَرَرْتُ: past-tense verb, built on sukūn with the attached subject pronoun تُ in the nominative position.
بِـ: preposition.
زَيْدٍ: noun governed in the genitive by bi-, with visible kasrah.
بِزَيْدٍ: prepositional phrase connected to the verb.
Do not mislabel Zaydin as a construct complement in this sentence: its direct governor is the preposition.