Reference: al-Muntaqaa min Fataawa Shaykh Saalih al-Fowzaan – Volume 5, Page 36, Fatwa No.48
Question: Is it permissible to perform the prayer on an area/place raised from the ground such as a bed or the like if a person had doubt about the purity (cleanliness) of the ground and there was no [Sharee’ah-based] excuse such as illness or the like [preventing him from praying directly on the ground]?
Response: There is no harm in a person praying on a raised area/place such as a bed or the like so long as it was pure (clean) and he was sure he would not experience any rocking/swaying or any interference in the prayer.