It is not permissible for a non-Muslim to pray either in the ranks or on his own. What he has to do is to enter Islam before he prays, then to purify himself by doing ghusl and then fulfil the conditions of prayer.

Prophet Muhammad said: “If any one of you feels drowsy when praying, let him sleep so that (when he gets up) he knows what he is reciting.” It may be understood that the degree of drowsiness referred to in the text is that where a person is unaware and does not understand what he is saying.