The book mentions زُفَر alongside عُمَر as examples of ʿadl + proper-name status.
حَضَرَ زُفَرُ — Zufar attended. «زُفَرُ» is the nominative subject.
سَلَّمْتُ عَلَى زُفَرَ — I greeted Zufar. «زُفَرَ» is genitive after ʿalā, with fatḥa as the case marker.
These two sentences are teaching examples; the book's passage lists the name rather than these sentences.