bismillaharrahmamarrahimOne of the most important etiquette and instruction is the recital of Surah al-Qadr (Power) before taking saheri and iftar as well as recital of illustrious and illuminated supplication:
"Allahuma rabb al-nur al-'adheem"
(Allah is the possessor of great illumination)
which has been given book of Iqbal written by the most esteemed and famous scholar Sayyid ibn Taoos. About this supplication it has been narrated from Imam al-Sadiq [a] that the Holy Prophet [s] has recommended recital of this prayer to Commander of the Faithful [s] hz 'Ali [ra] and said that Archangel Gabriel came to me and said:
"Whoever in the Holy Month of Ramadhan before iftar recites this prayer, Allah answers his prayer, accepts his prayer and fasting, grants his ten requirements, forgives his sins, removes his grief, makes his heart at ease, grants his wishes, makes his deeds to ascend upward with the deeds of prophets and righteous saints, and on the Day of Judgement brings him to His presence with a face illuminated like bright moon."
Comment
It becomes conspicuous from the narrations that fasting does not mean only abstinence from eating and drinking rather it also means renunciation of sins. Because, some of the sins like backbiting, lying, lustful sight, cursing, and oppression - be it less or more - would break the fast like the eating and drinking. Therefore, it is up to the fast observers to abstain from all the above, and during fast must endeavour so that eye, ear, tongue, hands, feet, and other bodily parts all together must observe fasting and should abstain themselves from performance of those acts which should not be performed, even they should avoid over-talking and should practice silence lest their fasting days do not have any difference with other days except eating and drinking, and they should not forget the words of the Holy Prophet [s], who has said:
"Renunciation of eating and drinking is the easiest thing - which has been made compulsory upon the fast observers."
And if, the scholars and jurisprudents consider the fasting of someone who has committed a portion of these sins - as correct, it is from this consideration that what they meant with this correctness of this fast is from the point of view of make up fasting (i.e. for some one, like this, it is not obligatory that after the Holy Month of Ramadhan he must repeat these fasts as makeup fasting). But what is meant with the correctness of fasting in traditions is - their acceptance by Allah (the Glorious, the Exalted). And in many cases a fast observer may undertake a fast in such a manner that in accordance with the religious decrees of a jurisprudent it would not be obligatory upon him to offer make-up (qadha) fast, but it may be that such fast would not have been acceptable by Allah (the Glorious, the Exalted).
The correct and perfect fast which Allah (the Glorious, the Exalted), has made obligatory for the self-perfection and spiritual ascent of fast observers, inevitably must be accompanied with abstinence from all bodily sins. Apart from that it would be much better if the fast observer in addition to renunciation of bodily sins should also practice abstinence from sins of the heart, i.e. should prevent the heart from any other remembrance except Allah's, and should renounce everything except Allah which is the most superior and esteemed fast.
Some one who has truly discovered the reality, virtues, and wisdom of fasting inevitably should abstain from all sort of sins and transgression for the sake of fast's acceptance, otherwise on the Judgement Day he would be questioned why his eyes, ears, tongue, and other bodily parts did not observe fasting? And simply quitting eating and drinking which would relieve him from undertaking make-up fasting (qadha) in this world, would not make him immune from scrutiny and Allah's punishment on the Judgement Day.

Surah Al Qadr