Exceptional circumstances

Dr. Muhammad Hedayetullah, scholar in comparative religion, in his book Dynamics of Islam (2006), stresses that even though salah is compulsory, flexibility in the specifics is allowed depending on the circumstances: For example, in the case of sickness or a lack of space, a worshipper can offer salah while sitting, or even lying down, and the prayer can be shortened when travelling. The salah must be performed in the Arabic language.