Source: The Great Interpretation of Dreams (Ibn Sirin)
(By analogy with fish and play) A dolphin may indicate a peaceful man who loves good, or it indicates good news and tidings coming from the direction of the water (travel or trade).
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
(By analogy) A dolphin may indicate salvation from drowning or hardships, or a loyal friend who helps in crises.
Source: Signs in the Science of Expressions (Ibn Shaheen)
(By analogy) A dolphin is interpreted as goodness, salvation, and joy.