Source: The Great Interpretation of Dreams (Ibn Sirin)
Breaking a pen in a dream indicates the death of a child or the loss of authority or knowledge.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
Breaking a pen indicates removal from a position or failure in a matter.
Source: Signs in the Science of Expressions (Ibn Shaheen)
Breaking a pen is interpreted as worry. Whoever sees his pen break will be afflicted with worry.