Islam agrees with the existence of evil eye. What is the treatment when one is affected by evil eye?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Imams Al Bukhari and Muslim reported in a sound Hadeeth that the Prophet said: “Evil eye is indeed true.”

Imam Muslim also reported that the Prophet said: "Evil eye is the truth and if anything could precede (have effect on) the predestination it would be evil eye, and if anybody asks you to perform Ghusl (or ablution) [to give him the water so that he may perform ablution to be cured from evil eye] then do so.”

The Prophet also said: “Evil eye is the truth, it could cause a mountain to be leveled to the earth.” [Ahmad]

So, these Ahadeeth and others are enough evidence that evil eye is true.

For more benefit on treatment of evil eye, please refer to Fataawa 3273, 7151, 32262, 223150, 82648 and 374689.

Allah knows best.