It is to be stated that the effect of an evil eye is a fact. This is supported by many proofs from revealed texts and reasoning. Imam al-Bukhari reported on the authority of Abu Hurayrah that the Prophet (peace and blessings be upon him) said, “The effect of an evil eye is a fact.”
however, the evil eye can never harm unless Allah wills so. Hence, it shouldn’t be a cause of fear or terror to anyone, for supreme power and might are for Almighty Allah alone and He is the Only One we should fear. It is in Him that we should seek protection against Satan and the evil eye. Both al-Bukhari and Muslim reported in their authentic collections that `Aa’ishah (may Allah be pleased with her) said: “The Messenger of Allah (peace and blessings be upon him) used to tell me to recite ruqyah for protection against the evil eye.
In this context, Dr. As-SayedNuh, professor of Hadith Sciences at Al-Azhar University, states: Islam draws a Muslim’s attention whenever he/she beholds something great. One should say: “Whatever Allah wills is done, no power save with Allah”. Allah Almighty says, (If only, when thou enteredst thy garden, thou hadst said: That which Allah wilteth (will come to pass)! There is no strength save in Allah!…) (Al-Kahf 18: 39)
the Prophet, peace and blessings be upon him, is reported to have said: “Upon beholding something attractive, try to recount allah’s glorification by saying, “Allah is Blessed!” or “May Allah bless you!” etc.
envy and the evil eye have a common factor in breeding contempt and hatred, and showing or feeling resentment of someone’s success or advantage. This is what the evil eye normally aims at.
Both are supported by many proofs from revealed texts and reasoning. However, they do not automatically affect a person and can never harm unless Allah wills so. Hence, they shouldn’t be a cause of fear or terror to anyone, for supreme power and might are for Almighty Allah alone and He is the Only One we should fear. It is in Him that we should seek protection against Satan and the evil eye.
Moreover, one should never, if they don’t have proof, accuse anyone of being envious or evil, for this may result in breeding contempt and discord among people.

As for precautionary measures against envy or the evil eye, one may do the following:
1- Seeking Allah’s protection against the evil eye and envy
this can be done by remembering Allah at all times and this is an impenetrable shield against Satan and his devils. Allah says: (Say: I seek refuge in the Lord of Daybreak. From the evil of that which He create. From the evil of the darkness when it is intense.And from the evil of malignant witchcra. And from the evil of the envier when he envieth.) (Al-Falaq 113)
2- Observing piety, showing obedience to Allah and forsaking sinful acts
allah says, (But if ye persevere and keep from evil their guile will never harm you. Lo! Allah is Surrounding what they do.) (Aal `Imraan 3:120)
the Prophet, peace and blessings be upon him, said to his cousin, `Abdullah bin `Abbas: “Observe Allah’s duties and He will protect you; be pious to Allah and He will always support you…”
(This Hadith is classed as authentic by At-Tirmidhi in his book As-Sunan under the chapter “Concerning the Day of Judgment)
3- Demonstrating patience and perseverance
this means that one should never show any sign of being affected by envy, nor should one get overwhelmed with thoughts on it. Rather, one should show patience, for that will definitely drive the envious or evil ones to doom.
In his commentary on the previous issue, Ibn Al-Qayyim states that the third precautionary measure against envy is to show patience rather than waging war against the envious or showing signs of being harmed by them. Nothing grieves or inflicts pain or even doom on the envious or evil one than seeing that his evil act or scheme has not affected the target. This is the effect of patience, rel
iance on Allah and putting one’s trust in Him. Allah says: (That (is so). And whoso hath retaliated with the like of that which he was made to suffer and then hath (again) been wronged, Allah will succour him. Lo! Allah verily is, Mild, Forgiving.‏) (AL-Hajj 22: 60)
In this Qur’anic verse, we can see that Allah has guaranteed victory for a victim of contempt or hatred, even if he has tried his best to avenge himself of the assailant. This means that a person who shows patience, despite being a victim of hatred and contempt, deserves strong support.
4- Putting one’s trust in Allah
This is one of the strong precautionary measures against envy and oppression. Allah says, (And whosoever putteth his trust in Allah, He will suffice him…‏) (At-Talaq 65: 3)
5- Sincere repentance to Allah.
If a person remembers the favors Allah has bestowed on him and returns everything that he has wrongfully taken from people with the resolve not to return to such a sin again, this will definitely bring him back to the right path. He will attain Allah’s forgiveness and this will drive him away from the evil eye. Allah Almighty says, (And turn unto Allah together, O believers, in order that ye may succeed. ) (An-Noor 24: 31)‏
6- Demonstrating a “turn the other cheek” gesture
this means that a victim of envy and the evil eye should try to be good to those who envy him or give him the evil eye. He should try to be good to them by speaking kindly, offering them gifts, feeding them and showing that he cares for them, as well as being a friend in need. Allah Almighty says, (The good deed and the evil deed are not alike. Repel the evil deed with one which is better, then lo! he, between whom and thee there was enmity (will become) as though he was a bosom friend.‏ But none is granted it save those who are steadfast, and none is granted it save the owner of great happiness.) (Fussilat 41: 34-35)
the point here is that showing good gestures to one’s foe can change him from an enemy to a friend.
7- Doing ruqya
this is based on the fact that the Angel Gabriel used to make du`a’ upon Prophet Muhammad (peace and blessings be upon him) whenever he became affected with anything.
`A’ishah (may Allah be pleased with her) says: “Angel Gabriel used to pronounce some words upon the Prophet (peace and blessings be upon him) to relieve his pain. He used to say: “May you get relief from the pain, cured from the disease, and be protected from envy and evil eye by the virtue of Allah’s Name.” (Reported by Muslim)
abu Sa`eed also mentions that the Angel Gabriel once came to the Prophet (peace and blessings be upon him) and asked him: “Are you affected with something?” The Prophet answered, “Yes”. Gabriel said: “May you get relief and be protected from evil by the virtue of Allah’s Name.” (Reported by Muslim)

8- Washing off the effects of envy
this is done by pouring the water on a person affected with envy and the evil eye.
this is based on the Hadith reported by Abu Umamah, Sahl bin Hunayf on the authority of his father who told him that as they went out one day with the Prophet (peace and blessings be upon him) upon reaching the valley called Al-Harar at Jahfah, Sahl washed himself and appeared as having a very fine figure. This attracted `AmiribnRabi`ah to the extent that he actually said: “Wow! What a nice and delicate figure! You look like a charming lady!” Upon uttering this remark, Sahl fell unconscious, and when the people took him to the Prophet, he said: “Do you suspect someone?” “Yes”, they replied, “We suspect `AmiribnRabi`ah“. The Prophet called him and reprimanded him, saying: “Why try to kill your brother in faith? Why not say upon seeing something fascinating: ‘Allah is Blessed or may Allah bless you…etc?’” To wash off the traces of envy, `Amir was told to wash his face, hands, elbows and thighs, and then to wash his feet and his private parts, over a bowl. Then the contents of this bowl were to be poured over Sahl bin Hunayf, and the bowl turned upside down. Upon doing this Sahl recovered.
(Classed as authentic by Imam Ahmad in Al-Musnad, and by IbnMajah)
Ibn Al-Qayim commented on this process saying:

Anyone who denies, mocks or has doubt about the effect of this Prophetic way of healing will never benefit from it. The same applies to anyone who does it in way of trial without full conviction. Why not regard this as part of the privileges in the Islamic perspective instead of condemning it. Medical practitioners acknowledge that in the field of medicine there are some areas that are untouchable and are somehow deemed as very unique.

IbnHajar says that the aforementioned process of washing away the effects of envy is meant to be done after being affected with envy.
Islam has also drawn attention to a precaution against that effect. This is what the Prophet means by ordering us to utter Allah’s Glorification when we have something good: ‘Allah is Blessed!’ Also we can supplicate for the person by saying: ‘May Allah bless you!’”