All praise is due to Allah, and may peace and blessings be upon the Messenger of Allah.
First: The effects of the evil eye and envy are established in the Quran and Sunnah.
The evil eye is real. The Prophet ﷺ authentically said:
"The evil eye is real, and if anything could precede divine decree, it would be the evil eye." Narrated by Muslim.
It is also authentically established that the Prophet ﷺ instructed people to perform ruqyah for the evil eye and approved treating the afflicted person by washing with the trace of the person who caused it.
Second: How do the evil eye and envy affect a person?
There are no religious texts that specify exactly how the evil eye affects a person. Ibn Al-Qayyim (may Allah have mercy on him) mentioned several explanations, clarifying that the influence of souls and spirits upon physical bodies is possible, and that envy may become a cause of harm by the permission of Allah Almighty.
Third: Does the effect of the evil eye and envy contradict divine decree?
There is no contradiction between them. Everything happens according to the decree of Allah Almighty. The evil eye and envy are among the causes through which Allah may bring about harm, and their effects occur only by His permission.
Allah Almighty says:
"But they cannot harm anyone through it except by Allah's permission." [Al-Baqarah: 102]
Fourth: Does Surah Al-Falaq protect against envy?
Yes. Surah Al-Falaq is among the greatest means of seeking refuge from the evil of the envious. Allah Almighty says:
"Say: I seek refuge in the Lord of daybreak, from the evil of what He has created, and from the evil of darkness when it settles, and from the evil of those who blow on knots, and from the evil of an envier when he envies." [Al-Falaq: 1–5]
Therefore, Muslims should regularly recite the morning and evening adhkar, recite the protective surahs, seek refuge in Allah from the evil of envious people, and turn to Him through Islamic ruqyah when afflicted.
Conclusion: The evil eye and envy are real and may cause harm, but they remain within the decree and will of Allah. A Muslim should take the prescribed means of protection and treatment while placing complete trust in Allah.
And Allah knows best.