How can a person know who has envied him, and how should the one who has been envied be treated?
Question

Is it possible for a person who has been affected by envy (hasad) to know whether the envy came from himself or from another person? What is the remedy in either case?.
Praise be to Allah.Firstly: 
If a person looks at something he has with admiration and he does not pray for barakah (blessing) for it, by saying “Baarik Allahu fihi (may Allah bless it)” and the like, and this thing is then affected in some way, then it is possible to know that he has inflicted hasad on himself.  
It is not possible to know that a specific person is the one who has envied you, except in circumstances such as those described above, such as if a person enters your shop and starts to admire it but does not pray for it to be blessed, then things in the shop get broken or damaged.
 This applies in cases where the effect is seen straightaway. But if a long time passes before something happens, then we cannot be certain that a specific person has envied him. 
There are means that some people use to find out who has put the evil eye on something or someone, but these are not prescribed or approved of in sharee’ah, rather they are devilish means, such as imagining (the person who caused it) during recitation of Qur’aan as a remedy, or seeking the help of the jinn and devils (shayaateen) to find out such things. 
The scholars of the Standing Committee said: 
With regard to imagining (the person who caused it) during recitation of Qur’aan as a remedy, this is a devilish procedure which is not permitted, because it is seeking the help of the devils (shayaateen), who appear to the sick person in the form of the one who afflicted him. This is something that is haraam, because it involves seeking the help of the devils, and because it stirs up enmity between the people, and spreads fear and mistrust among people, so it comes under the verse in which Allah says (interpretation of the meaning): 
“And verily, there were men among mankind who took shelter with the males among the jinn, but they (jinn) increased them (mankind) in sin and transgression”
[al-Jinn 72:6]
They said: It is not permissible to seek the help of the jinn in order to find out what has been done and how it should be treated, because seeking the help of the jinn is shirk. Allah says (interpretation of the meaning): 
“And verily, there were men among mankind who took shelter with the males among the jinn, but they (jinn) increased them (mankind) in sin and transgression”
[al-Jinn 72:6]
And He says (interpretation of the meaning): 
 
“And on the Day when He will gather them (all) together (and say): ‘O you assembly of jinn! Many did you mislead of men,’ and their Awliyaa’ (friends and helpers) amongst men will say: ‘Our Lord! We benefited one from the other, but now we have reached our appointed term which You did appoint for us.’ He will say: ‘The Fire be your dwelling place, you will dwell therein forever, except as Allah may will. Certainly your Lord is All-Wise, All-Knowing’”
[al-An’aam 6:128]
What is meant by benefiting from one another is that the humans venerated the jinn and humbled themselves to them and sought their help, so the jinn served them and did what they wanted, and brought them what they asked for – including telling them the nature and causes of sickness, things which the jinn can see but humans cannot. But they may tell them lies because they cannot be trusted and it is not permissible to believe them. 
 Majallat al-Da’wah, no. 1682. 
Secondly: 
With regard to treating one who has been affected by envy, there are two ways of doing this: 
If the person who envied him is known, he may be asked to do ghusl and the water used should then be poured on the “victim”. If he is not known then the remedy is by means of ruqyah and the dhikrs prescribed in sharee’ah. 
For more details on the evil eye and envy (hasad), and the differences between them, and how to protect oneself against them, please see the answers to questions no. 20954. 7190, 11359, 12205.