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, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
You should know that khushoo’ (i.e. state of the heart when it stands before its Lord in full submission, humility, and absolute concentration) in prayer is one of the most important things that a Muslim should try to attain because it is the essence and core of the prayer. Therefore, you should strive to attain khushoo’ through supplication and by repelling any worldly thoughts whenever they occur to your mind.
However, failure to attain khushoo’ does not affect the validity of your prayer, nor does it entail repeating it although you do not earn the full reward for the prayer if you fail to attain perfect khushoo’.
There is no harm in pausing a few seconds before tasleem (concluding the prayer), and this does not affect the validity of the prayer.
For more benefit, please refer to fataawa 85048, 88068 and 82335.
Allaah knows best.