حَيَّ عَلَى الْفَلَاحِ
Come toward success.
“حَيَّ” is an imperative ism fiʿl, roughly equivalent in meaning to “أَقْبِلْ” or “هَلُمَّ.” It is not an ordinary conjugated imperative verb, yet it performs the semantic work of calling someone toward an action.
عَلَى الْفَلَاحِ: a prepositional phrase indicating the desired goal or direction; “الْفَلَاحِ” is genitive.
The phrase is familiar from the adhān. The important distinction is between grammatical classification as an ism fiʿl and rhetorical force as a directive. A noun may carry command-like meaning.