Is working in faith a condition for perfection or a condition for validity, and what is the proof for that?

The servant is obligated to obey Allah completely, outwardly and inwardly. However, one who abandons deeds does not disbelieve unless he commits something that contradicts Tawhid (monotheism). This is what is indicated by the hadiths which state that whoever says "La ilaha illa Allah" (There is no god but Allah) will emerge from the Fire and will not remain in it eternally.

The Companions unanimously agreed that abandoning deeds other than prayer does not constitute disbelief. The majority of jurists do not consider abandoning prayer to be disbelief, but rather a grave sin (fisq). This is what jurists have inferred from matters of inheritance, burial, and other issues.