Excerpts from the original by Ayatullah Khomeini
Contributed by Jameel Kermalli (Sanford, United States)
And if the practice of that glorious Sayyid is ‘tot it binding proof (hujjah) for you, the practice of the Master of Monotheists (Sayyid alMuwahhidin, i.e. the Prophet [S]) and his infallible descendants is, of course, a hujjah for you. Study the condition of those noble souls and the character of their worship and prayers. At the time of salat the colour of their blessed faces would pale and their bodies would tremble with the fear lest there should occur some lapse in the course of this divine observance, although they were infallible.
It is well-known concerning the Mawla (‘Ali) that ail arrow that had pierced his blessed foot and removing which was intolerably painful for him, was taken out when he was engaged in salat and he did not even notice its removal.
My dear, such a thing is not impossible. Such things occur quite often for people in the ordinary course of life. At times a man becomes totally oblivious of everything in the state of anger or love. One of our reliable friends used to narrate that “Once during a fight with a group of ruffians in Isfahan, I noticed that some of them struck me with their fists and I did not know what kind of blows they were. Later when the fight was over and I came to myself, I realized that. I had several wounds made by a knife with which they had struck me. I was bedridden for several days before I recovered from those wounds.” Of course, the reason behind it is obvious: when the total attention of the soul is concentrated on a certain matter, it becomes totally oblivious of the body and insensitive to its feelings. All its attention is absorbed by that single thing.
In our own fights, encounters or heated debates in a gathering-may God be our refuge from these-we have often noticed that we become totally heedless of everything else that takes place around us. However, regrettably, everything absorbs our total attention except the worship of the Lord, and that is why we tend to regard such episodes (as that of Imam ‘Ali) as improbable.
In any case, detachment of the heart from everything except God is an important matter and one must try to attain it at all costs. The means of achieving it is also possible and attainable. It can be achieved with the exercise of some care and vigilance. One should make effort for some time to bring the flights of the bird of his thought under control and restrain it whenever it wishes to fly from one branch to another. After a period of watchfulness, the mind becomes tractable and docile and refrains from engaging in random thoughts. In accord with the aphorism -goodness becomes a habit with it and, attaining detachment from other preoccupations, it becomes attentive to God and His worship.
Of foremost importance amongst the prerequisites of worship is the attention of the heart, on which depends the soul and essence of worship and without which it has no value and acceptability near God, the Exalted, as mentioned in sacred traditions.
In al-Kafi, al-Kulayni reports with his isnad from Abu Ja’far and Abu ‘Abd Allah-may peace be upon them-that they said to Fudayl ibn Yasar: “The reward that you derive from your salat is limited to the extent that you offer it with an attentive heart. And if someone should vitiate all of it or neglect its etiquette, it is wound up and thrown at the face of its offerer.” 
Al-Shaykh Muhammad ibn al-Hasan (al-Tusi)-may God be pleased with him -reports in al-Tahdhib with his isnad from Abu Hamzah al-Thumali that he said: “I saw ‘Ali ibn al-Husayn (al-‘Imam al-Sajjad) may peace be upon both of them-offering prayer, when the cloak slipped from his shoulders. The Imam did not arrange it until he had finished his prayer. When I questioned him about it, he said:
‘Woe to you, don’t you know before whom I stood? Nothing is accepted of a devotee’s prayer except what he offers with the proper attention of his heart.’ Thereupon I said to him, ‘May I be ransomed for you, (if that is so) then we (i.e. the like of us) are doomed!’ He replied, ‘No indeed. Verily God compensates for that for the faithful by the means of supererogatory prayers.’ ” 
In al-Khisal, (al-Shaykh al-Saduq) reports with his isnad from ‘Ali-may peace be upon him-that he said: “None of you should ever stand for salat in a lazy or drowsy state, nor should you let (random) thoughts pass through your mind (in the state of salat). For, in that state, you stand before your Glorious and Almighty Lord. Verily, the reward a devotee derives from prayer is equal to the extent of it that he offers with an attentive heart.” 
There are many traditions on this theme and concerning the merit of attentiveness. Here we will cite some of them which are sufficient for those who will take lesson.
Muhammad ibn ‘Ali ibn al-Husayn, the saduq of the community, reports with his isnad from ‘Abd Allah ibn Abi Ya’fur that al-‘Imam al-Sadiq-may peace be upon him-said to him, “O ‘Abd Allah, when you offer salat, pray like someone who bids farewell and fears that he will never return (i.e. pray in such a manner as if it were the last prayer of your life). Then fix your gaze on the point of your prostration. If you know that there is someone on your left or right, you take more care in offering your salat; then know that you stand in front of Someone Who sees you and you don’t see Him.” 
Al-‘Imam al-Sadiq-may peace be upon him-said: “Dear to me is the believer from among you who attends to God with his heart at the time of prayer and does not preoccupy his heart with any mundane matter. For whenever a devotee turns with his heart to God, the Exalted, during prayer, God turns His face towards him, and turns towards him the hearts of the faithful who regard him with affection, following God’s love of him.