The Ruling Concerning Putting a Knife On a Child in Order to Protect Him
I have seen some people placing a knife on their small children and saying, “This is so the jinn do not come to him.” Is this practice correct?
This is an objectionable act and there is no sound source for it. It is not allowed to do such a thing. What is legally sanctioned is to seek refuge from them by Allah’s complete words from every devil and poisonous pest, as has been confirmed from the Prophet (peace be upon him). He used to seek protection by those words for his grandsons al-Hasan and al-Husain Ibn Ali. It is also sanctioned to make dua for them by asking Allah to protect them from every evil. As for putting a knife or something similar, of iron, wood or other substances, with the belief that such will protect them from the jinn, it is an evil practice that is not allowed.
Similar is the ruling with respect to hanging an amulet over them, which is what is called al-tama’im. This is not allowed because the Prophet (peace be upon him) said,
“Whoever hangs an amulet, Allah will not complete[his affair] for him” 
In another narration, the Prophet (peace be upon him) said,
“Whoever wears an amulet has committed shirk.” 
May Allah bestow understanding of the religion upon all Muslims, and steadfastness in the religion. We seek refuge for ourselves and them3 from everything that differs from His pure law.
Shaikh Ibn Baz
1. Recorded by Ahmad, Ibn Hibban and others. Salih al-Usaimi concludes that it is hasan. See Salih Ibn Abdullah al-Usaimi, al-Dural-Nadheed fi Takhreej Kitab al-Tauheed (Dar ibn Khuzaima, 1413 A.H.), p. 38.– JZ
2. Recorded by Ahmad and al-Hakim. Al-Usaimi also concludes that this hadith is hasan. See al-Usaimi, p. 39.– JZ
3. In English, the more proper manner is to invoke for others first and then for oneself. However, in Arabic, the opposite is considered the proper manner of speech.– JZ
Source : Islamic Fatawa Regarding Women
Author: Muhammad bin Abdul-Aziz Al-Musnad, Pages: 391
Publisher : Darussalam – [Buy]