If a person is feeling jealous, what should they do? And how should they react? What should they understand and what form of Ibadah (worship) should they do in connection to jealousy?
If you feel jealousy then you have to give him gifts and shake hands with him, as proved from this hadith:
The Prophet said: “Shake hands, for this will dispel rancour, and exchange gifts and love one another, for this will dispel hatred.” (Narrated by Maalik in al-Muwatta’, 1413).
Prophet Muhammad also said:
“You will not enter Paradise until you believe, and you will not believe until you love one another. Shall I not tell you of that which will strengthen love between you? Spread (the greeting of) salaam amongst yourselves.” (Narrated by Muslim, 81).
Also Shaykh al-Islam Ibn Taymiyah said in his book Amraad al-Quloob (diseases of the heart):
Whoever find in himself any hasad towards another has to try to neutralize it by means of taqwa (piety, consciousness of Allaah) and sabr (patience). So he should hate that (the feeling of hasad) in himself… But the one who does wrong to his brother by word or deed will be punished for that. The one who fears Allaah and is patient, however, is not included among the wrongdoers, and Allaah will benefit him by his taqwa.
If you need more details, then you can refer here: http://islamqa.info/en/12205
I had decided to answer this question based on the guidelines by Imam Ayatollah Ruhollah Khomeini who is considered one of the most prominent authorities and epitomes of practical ethics among revolutionary Shias. But it took a while to prepare the answer for Imam's ethical discussions are usually very profound, substantive and nuanced. I hope the answer is useful and inspirational to readers.
First, it is worthwhile noting that Ayatollah Khomeini was a grand scholar of fiqh, ethics, philosophy and Irfan (Shia brand of Islamic Mysticism) who also successfully led the glorious Islamic Revolution of Iran in 1979.1
One of his famous books on ethics and beliefs is his holiness's Exposition of Forty Hadiths. The book as the title suggests is an exposition of forty hadiths by the Holy Prophet and His Purified Household (peace be upon them). The hadiths involve ethics and beliefs discussed by the profound wisdom of Islamic Mysticism.
Muhammad ibn Ya’qub (al-Kulayni), from ‘Ali ibn Ibrahim, from Muhammad ibn ‘Isa, from Yunus, from Dawud al-Raqqi, who reports from Abu ‘Abd Allah (Imam al-Sadiq) (A) that the Apostle of God (S) said that God Almighty addressed Musa ibn ‘Imran (A) thus: “O son of ‘Imran, never be jealous of people concerning the favors I have conferred on them by My grace, do not glower at them, and do not succumb to your (jealous) ego. Indeed the jealous is indignant at the bestowal of My favor, and contests My apportioning of gifts among My creatures. Whoso is such, he neither belongs to Me nor do I belong to him.” Usul al-Kafi, vol. 2. p. 307
[The translation is taken from the linked chapter above with minor modifications, the main being replacing envy with jealousy for I found latter alternative to be closer to Imam's concept of hasad]
In what follows I try to summarize the main theses and guidelines of Imam while making a few commentaries and notes of my own for elucidating particular philosophical wisdom behind some of the Imam's theses.
Nature, causes and effects of hasad
Imam defines hasad as when a person desires deprivation of someone from a positive quality or s/he possesses. Imam postulates various kinds and degrees for jealousy depending on 1) the conditions of mahsud (the object of jealousy) which varies from the person's enjoyment of intellectual/spiritual/moral virtues, to good deeds and even profane advantages; 2) the conditions of hasid (the jealous) which is about the causes of jealousy e.g. enmity, arrogance, fear, wonder, etc; and above all 3) the essence of jealousy itself. Later he suggests remedies for jealousy with regards to some of these factors.
In general Imam argues that feeling of inferiority or disadvantage by the self is the root cause of all forms of envy and jealousy.
One of the interesting points that Imam makes in his exposition of jealousy — that can be very helpful in treating some forms of this moral vice — is that the jealous could be deluded in his jealousy, and this happens when the object of jealousy in a person is not in reality a real virtue or merit to justify envy (let alone jealousy) at all. So such form of jealousy would be indicative of an additional defect: ignorance of real virtues from false virtues. An example of delusional jealousy is when someone is envied for being garrulous or facetious, or for being feared as a bully. None of these characteristics are virtues to warrant jealousy in the first place. They are in fact vices that must be deplored and avoided.
Imam also exhorts us to contemplate the fact that jealousy doesn’t harm the person we feel jealous of! It doesn’t take away from the person the perceived advantage he enjoys that has provoked our jealousy. On the contrary, our jealousy might even strengthen the person’s pride and self-satisfaction, leading to our further irritation! With such contemplations, Imam tries to persuade us that there’s much harm and no benefit really in being jealous. The person affected by this vice always suffers a state of spite and grudge which negatively impacts his physiological health and mental peace.
To explain the spiritual harms of jealousy, Ayatollah Khomeini quotes another hadith from Imam al-Sadiq (PBUH): “... jealousy devours faith as fire devours woods”. He explains this by linking jealousy to dissatisfaction with Divine justice and determinations, which indicates lack of real faith in justice of Allah.
The difference between professed doctrine and enlightened faith
This condition, that is the conflict between one's professed beliefs and actual sentiments, Imam argues, can affect the apparently most pious and learned of religious scholars. A Muslim theologian afflicted by grave calamities could find himself upset with his destiny, despite the fact that as a scholar he had argued and preached much of his life in support of the belief that Allah is all-benevolent and that His creation is the best of all possibilities and His destinations always just. Such a man, Imam argues, “counters his own words and confutes his own arguments” for his beliefs “do not go beyond words and have not entered the heart.” Imam also holds that all moral vices by "believers" are rooted in this common but widely unidentified or neglected defect.
Raising awareness about this common contradiction between one’s actual sentiments about Allah’s determinations in real life situations and one’s proclaimed beliefs in Him is a recurring theme in Imam’s ethical works. He explains this contradiction by distinguishing between rational confirmation of an Islamic doctrine (or a philosophical truth in general) which is done by the virtue of one’s reason and mind, and intuitive realization of the ‘truth’ of the doctrine by one’s heart.2 Therefore one doesn’t qualify as a faithful believer by simply proclaiming religious beliefs, but only when he has realized the truth of the beliefs via contemplation, self-purification and ultimately reaching the level of Ridha or full contentment with all Divine decrees and determinations. Only then the person would be able to stand true to his beliefs in the face of trials and calamities.3
Further expanding on the vices of jealousy, Imam states that jealousy stiffens and depresses the heart, while a believer has to keep an expansive and lively heart for Divine Grace. A believer is humble, genial and kind, while jealousy generates the exact opposite of these moral traits.
Practical cure for jealousy
As a practical approach to combat jealousy Imam recommends defying the vice by doing the exact opposite of what it naturally inclines the afflicted person to do. That is, treating the envied person with love and admiration instead of being hurtful towards him/her. This, Imam admits, is a difficult undertaking since it goes against one’s ego and its active condition, but a conscious, steadfast struggle against the ego while reminding one’s self about Divine just and grace towards all creation would gradually weaken and subdue the vice until the afflicted person finds real, sincere satisfaction in seeing a fellow enjoying a greater share of Allah's favors.
1. And that's what makes Imam Khomeini special in my eyes even among the scholars equal to his rank in terms of vast comprehensive knowledge: Apart from his lofty scholarly credentials, Imam could inspire and lead an epoch-making mass revolution that liberated Iran from the corrupt rule of the secular despotic Pahlavi Monarchy and has now turned Iran to a positive influential force for peace and security in a region torn by Western military interventions and imperialist plots. In this impressive achievement, Imam's close affinity with wisdom of Allah and the transcendental had definitely a substantial role.
2. The ‘truth’ corresponding to a theological/philosophical doctrine according to Imam’s underlying metaphysical axioms, is an actual spiritual entity in the spiritual world. This idea is based on a highly improved notion of the Platonic Theory of Forms by Mulla Sadra (+ +), the most prominent metaphysician in Shia scholastic history. Mulla Sadra argued that for abstract philosophical truths expressed in conceptual and propositional terms, there are actual reference points in the form of active incorporeal beings in the spiritual world for which their corresponding abstract concepts are only "ambiguous shadows". While the mind of a philosopher can realize the conceptual representations by exercise of reason, the realization of their actual incorporeal principles is a matter of practical psychic/spiritual perfection. This theory serves as a philosophical support for the duality between knowledge (as possessed by mind) and "faith" (as enjoyed by heart) in religions.
3. Imam Khomeini himself was indeed a high epitome of steadfast confidence and commitment in his religious beliefs shown in his tireless faith-inspired struggles against Pahlavi Monarchy despite all the dangers, calamities and disappointments that he faced along the long course of his revolutionary efforts for 26 years.