This question is from Abu-Umar, from Damascus: Sometimes, as soon as I mention a blessing Allah has bestowed on a relative or a friend, some people knock on wood. They do that as an expression of fear of the evil eye. In some instances, they demand of one to knock on wood by saying: “Knock on wood”. What is the validity of such behaviour? Please advise us. May Allah reward you.
Answer by Shaykh Ibn Baz:
This is reprehensible behaviour, which must not be done, and the underlying belief is corrupt. Instead, when a person gains a blessing, he has to thank Allah for it, and to beg Him to perfect that blessing and make him grateful. Allah says,
<<And when your Lord proclaimed: If ye give thanks, I will give you more; but if ye are thankless, lo! My punishment is dire>>. [Ibraheem Sura, Ayah No. 70]
He also says,
<<Therefore remember Me, I will remember you. Give thanks to Me, and reject not Me>>. [Al-Baqara Sura, Ayah No. 152]
May Allah grant success to all of us.
Source : Ibn-Baz’s Collection of Fatwas and Articles, Vol. 8, p. 424