Source: The Great Interpretation of Dreams (Ibn Sirin)
A nail in a dream is a mediator between people. Hammering it indicates marriage or completing a matter.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
A nail indicates a brother or a son. Whoever sees himself finding a nail will be blessed with a son.
Source: Signs in the Science of Expressions (Ibn Shaheen)
A nail is interpreted as goodness. Whoever sees himself hammering it will attain goodness.