'So woe to the praying ones, Who are unmindful of their prayers' [107:4]
The Ahlul bayt (a) are reported to have said:
'You have no share from your prayer
Save that portion in which you maintained the attention of your heart.'
Mawla al-Naraqi in Jami' al-Sa'adat says:
'How can the presence of the heart and the expression of humility not be the spirit of the prayer and (how can) the perfection of prayer not depend upon them, while the worshipper (musalli) in his prayer and supplication whispers to his Lord?
There is no doubt that speech along with absent-mindedness is not the act of whispering.
In addition, speech is an expression of what is in the heart or mind, and this is impossible save by means of the attention of the heart; for what (really) does the supplicant ask when he says: 'Guide us on the straight path' while the heart is inattentive?
And there is no doubt also that the purpose behind Qur'an-recitation and invocations (adhkar) is the act of laudation, praise, the expression of one's humility and supplication while the addressee is the Almighty Allah.
If the heart of the servant, therefore, was veiled from Him by the curtain of inattentiveness, and did not see or witness Him, but rather was inattentive of the addressee, and he moved his tongue out of (mere) habit, how remote then, is this, from the purpose behind prayer which was legislated for the refinement of the heart and renewal of one's remembrance of God...'