Source: The Great Interpretation of Dreams (Ibn Sirin)
Drinking poison in a dream, if it does not harm the dreamer, indicates gaining wealth or long life.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
Drinking poison and not dying from it indicates piety and devotion, or salvation from worry.
Source: Signs in the Science of Expressions (Ibn Shaheen)
Drinking poison and not dying is interpreted as salvation from worry or wealth.