All praise is due to Allah, and may peace and blessings be upon the Messenger of Allah.
The evil eye is real, and the permissibility of washing with the trace of the person who caused it has been established in the Prophetic Sunnah. Aisha (may Allah be pleased with her) reported:
"The person who caused the evil eye would be instructed to perform ablution, and then the person afflicted would wash with that water." Narrated by Abu Dawud and authenticated by Al-Albani.
First: How to obtain the trace of the person who caused the evil eye
It is permissible to obtain a trace of something that has come into contact with the person's body, such as their clothing, the remaining drink in their cup, or objects that their mouth has touched. This trace is then placed in water, which can be used for drinking or washing. Scholars have mentioned the benefit of this practice based on experience.
Second: Ruling on reusing the trace
If some of the person's trace remains, or some of the water in which it was placed is left over, there is no harm in using it again. It is not necessary to obtain a new trace as long as the original trace is still available.
Third: Ruling on repeating the washing
It is permissible to repeat washing with the trace of the person who caused the evil eye, whether the evil eye has occurred repeatedly or the washing is being repeated for the same affliction.
There is no specific number established in Islamic law for repeating this washing, as long as it is beneficial and does not cause harm.
One should not rely on this alone, but should also maintain Islamic ruqyah, regular remembrance of Allah, and authentic supplications, while firmly believing that healing is in the hands of Allah alone.
We ask Allah Almighty to heal everyone who is afflicted and protect everyone from the evil eye and envy.
And Allah knows best.