People are divided into five categories when it comes to performing Salaah:
1– There are those who wrong themselves by failing to perform Wudu’ perfectly, or to pray at the prescribed times of Salaah, ignoring its Arkaan (essential ingredients).
2– There are those who perform Salaah on time, make perfect Wudu’, and maintain its Arkaan; however, they lose their concentration during Salaah (Khushu by listening to Satan’s whisperings).
3– There are those who perform Wudu’ perfectly, concentrating during Salaah, but they constantly battle against Satan’s whisperings and insinuations, in order to prevent him from stealing their Salaah; these people are performing both Salaah and Jihad against Satan.
4– There are those who perform Salaah with complete submission to Allah. After they have completed Wudu’, their hearts have fully surrendered to the worship of Allah, and they forget about worldly affairs.
5– There are those who perform Salaah with complete submission, sincerely focusing their hearts and minds on Allah, fearing and loving Him, as if they were looking at Him; Satan cannot whisper to them, for they are contemplating their Lord. The difference between these people and others with regard to Salaah is far greater than the distance between the heaven and the earth. In short, they are closer to Allah in Salaah than at any other time.
The first type will be punished for their poor Salaah.
The second will be held accountable for it.
The third will have their sins forgiven for it.
The fourth will be rewarded for it.
The fifth will become close to Allah, because they concentrate on Salaah with their hearts and minds; they subdue their desire’ and Satan’s whisperings.
source: Expelling Jinn From Your Home, by Majdi Muhammad Ash-Shahawi, pages 50-51