Taweez

Taweez
The defenition of a ta'wiz is simply, a written du'a from the Qur'an or ahadith, and is for the one who cannot read or has not memorized that particular du'a. It is written on a piece of paper and is worn around the neck.
We, the Ahl as-Sunna, believe that to wear a ta'wiz around the neck is permissible if the du'a' contained in it is written from the Qur'an or ahadith. Prophet Muhammad (may Allah bless him and grant him peace) used to recite du'a' and then blow onto the sick person. The Companions of the Prophet (may Allah bless him and grant him peace) also did this and they wrote the du'a' on a piece of paper and placed it around the neck of a person if they could not read it. Of course, the du'a's from the Qur'an and ahadith have the power to heal the sick. Some people say that if you wear the ta'wiz you are commiting shirk, but we shall prove, with the help of Allah, that it is permissible to wear a ta'wiz.
The Qur'an Has the Power of Healing
Allah Most High says in the Qur'an:
"...We send down in Qur'an that which is a healing and a mercy to the believers..."

[Sura Banu Isra'il, verse 82]

Qadi Shawkani writes, "If the Qur'an's du'a's are recited and blown on the sick, they will be cured. When the non-believers recite the Qur'an, their blasphemic disease will be cured" [Tafsir Fath al-Qadir, under Sura Bani Isra'il, verse 82]

Proof of Wearing the ta'wiz

Hafiz Ibn Kathir and Qadi Shawkani write:
"Amr ibn Shu'aib (may Allah be pleased with him) said that 'Rasulu'llah(may Allah bless him and grant him peace) taught my father and grandfather a du'a which we would read before going to sleep, to protect us from fear and anguish.We told our elder children to recite this du'a before going to sleep as well.But for those children who were not yet literate, we would write it and then put it around their necks"

[Musnad Ahmad ibn Hanbal vol.2; Abu Dawud, in 'Chapter of Medicine'; Tafsir Ibn Kathir, under Sura al-Mu'minun, verse 97; and Qadi Shawkani, Fath al-Qadir, under the same verse]

It is Permissible to Read Du'a and Blow Upon the Sick
Imam al-Bukhari and Imam Muslim write:
"When a person who was sick or in some distress they would go to the Prophet (may Allah bless him and grant him peace) who would then place his hand on the area of pain and recite a du'a' and then blow onto him"

[Bukhari; Muslim, Chapter of Tibb]

Imam Muslim writes:
"When the Prophet (may Allah bless him and grant him peace) was ill for the last time, Angel Jibril (peace be upon him) came and recited du'a' and blew on to the Prophet (may Allah bless him and grant him peace)"

[Muslim, Chapter of Tibb]

Imam Muslim writes:
" 'A'isha (may Allah be pleased with her) relates that when the Prophet (may Allah bless him and grant him peace) was ill for the last time, she recited Sura al-Falaq and Sura an-Nas and then blew on to the Prophet's  (may Allah bless him and grant him peace) hands. The Prophet then blew this onto his own face and body because his hands had more blessing then 'A'isha's (may Allah be pleased with her)"

[Muslim, Chapter of Tibb]

From the above narrations, it proves that to blow after reciting du'a's onto the sick is Sunna and the more pious the person is, the more healing power he has because he is blessed more than the less pious.
Hafiz Ibn Taymiyya writes:
"It is permissible to [to recite du'a's and then] blow upon the sick in Islam, but the words must be from the Qur'an or ahadith. If the words are not, then it is not permissible"

[Ibn Taymiyya, At-Tawassul, Chapter on Blowing onto the Sick]

Questions

Q) Some people ask, 'How is it allowed to blow dua's onto the sick when some ahadith say this is forbidden?'
A) Allama Sa'idi has written the answer to this question in great detail; he has also included the opinion of all the other great scholars, and we will present this here.
Allama Sa'idi writes:
"Imam an-Nawawi in Sharh Muslim states: 'There are two types of ahadith concerning blowing. [reciting a du'a and then blowing onto a person]. One of the types is transmitted in Bukhari: 'There will be people who will enter Paradise without any questioning, who have never been blown upon.' Imam Muslim has also recorded a hadith in support of those who do not ask to be blown upon. Imam Bukhari in the chapter on Tibb [Medicine] has written du'as that our Prophet (may Allah bless him and grant him peace) recited when doing damm [reciting a du'a and then blowing onto a person]. Imam Muslim states in 'The Chapter on Virtues of the Prophet (may Allah bless him and grant him peace)' that: "When our Prophet (may Allah bless him and grant him peace) was ill, the Angel Jibril came to him and performed the blowing." The above types of ahadith apparently seem to contradict each other but in reality there is no contradiction.
"The former type of hadith refers to the prohibition of having read something that is not from the Qur'an and Sunna [i.e.something that has pictures, diagrams or words not from the Qur'an or Sunna] and then blow upon someone. The latter types of ahadith which permit damm refer to those kalimat [words or verses] which have been taught by the Prophet (may Allah bless him and grant him peace)"

[Allama Sa'idi, Sharh Sahih Muslim, Chapter of Tibb]

In the same way as above there are two types of ahadith concerning ta'wiz. There are many narrations that forbid the use of ta'wiz and also many permitting their use.
Imam al-Qurtubi wrote in detail about both types of ahadith concerning ta'wiz:
"The ta'wiz that are forbidden are those ta'wiz from the Time of Ignorance - those which are satanic and contain an element of shirk [mantar, voodoo and magic, etc.]. The ta'wiz, which are permitted are those written with du'as evidently from Qur'an and ahadith only"

[al-Qurtubi, at-Tadhkirat, chapter on 'Ta'wiz']

Here are the narrations which show the permission for one to wear a ta'wiz around one's neck:
Allama Alusi al-Hanafi, in his Tafsir of the Qur'an, writes:
"According to Imam Malik 'It is permitted to put around the neck the ta'wiz written with the name of Allah.' Imam Baqir also stated that it is permitted to put such a ta'wiz around the neck of a child"

[Ruh al-Mani, chapter 15, under Sura al-Mu'minun, verse 97]

Allama Shami al-Hanafi writes:

"It is permitted to write a ta'wiz and put it around the neck... It would be better if a person recites the du'as taught by the Prophet (may Allah bless him and grant him peace). But if a person cannot read or is too young to recite then it is permitted for that person to put it around the neck"

[Rad al-Mukhtar, chapter on 'Qira'at'; Sa'idi, Sharh Sahih Muslim, Chapter on Tibb]

To conclude, it can be said that those verses that oppose the Qur'an, Shari'a, or the Sunna are forbidden to read and also forbidden to put around the neck.But as for the du'as and verses from the Qur'an and Sunna it is permitted to be written and put around the neck of a small child, illiterate or a sick person