All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
An individual offering prayer has to concentrate in his prayer so as to attain contemplation as well as Khushoo' which is the essence of the prayer. The Muslim must not surrender himself to thoughts and imaginations which only lead to the insinuations of the devil and wasting time. However, contemplating the universal Signs of Allaah The Exalted as well as occupying oneself with the remembrance of Allaah The Exalted and the Quran are matters that are more worthy of time being spent on them by a Muslim.
The individual who fulfilled the pillars and conditions of the prayer but lacks Khushoo‘ is not obliged to make it up even though he was almost unconscious of it. However, the reward decreases significantly in the absence of reverence. ‘Ammaar ibn Yaasir reported that the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said: “A person turns away from his prayer whereas it is not written in his account except one tenth or one ninth or one eighth or one seventh or one sixth or one fifth or one fourth or one third or half.” [Abu Daawood].
Allaah Knows best.