Hawzah News Agency – The place where the worshipper performs his canonic prayer must be motionless, such that the body of the worshipper remains still and stable throughout the prayer. Praying in situations where the worshipper’s body experiences involuntary motion—such as in a car or on a spring mattress—is invalid, unless one has no other choice on account of being short of time or other constraining reasons.

Source: https://www.leader.ir/en/book/32/Practical-Laws-of-Islam