Prayer: A Person Who Performs Prayers Sitting or Lying Down
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1436
A person who performs prayers sitting can follow someone who performs prayers sitting. However, it is problematic [i.e. based on obligatory precaution, it is not correct] for someone who performs prayers lying down to join congregational prayers, irrespective of whether the imam performs prayers standing, sitting, or lying down.