Source: The Great Interpretation of Dreams (Ibn Sirin)
Praying while sitting in a dream without an excuse indicates the non-acceptance of the deed or negligence in it.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
Praying while sitting for a sick person indicates the approach of his end or the prolongation of his illness.
Source: Signs in the Science of Expressions (Ibn Shaheen)
Praying while sitting is interpreted as weakness and negligence.