Source: The Great Interpretation of Dreams (Ibn Sirin)
A gecko in a dream is a slandering man who enjoins evil and forbids good. Killing it indicates triumph over a bad man.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
A gecko indicates a weak enemy. Seeing it indicates worry and grief.
Source: Signs in the Science of Expressions (Ibn Shaheen)
A gecko is interpreted as worry. Whoever sees himself killing it, his worry will vanish.