Ta'awwuz
Ta'awwudh [تعوذ], a verbal noun in Arabic, refers to seeking protect with Allaah [from the devil].
When it is said Ta'awwadha bi Allaah [تَعَوَّذَ بِاللَّهِ], it means that: He said: 'Auudhu bi Allaah min al-Shaitaan al-Rajeem [I seek refuge with Allaah from the accursed devil]
Allaah says in the Qur'aan:
So when you recite the Qur'an, [first] seek refuge in Allah from Satan, the expelled [from His mercy].
[Qur'aan 16:98]
The wordings for Ta'awwuz
The wordings used, which are authenticated from Hadith, include:
أَعُوذُ بِاللَّهِ السَّمِيعِ الْعَلِيمِ مِنَ الشَّيْطَانِ الرَّجِيمِ مِنْ هَمْزِهِ وَنَفْخِهِ وَنَفْثِهِ
The above wording is present in the following Hadith:
The Prophet (sallallaahu alayhi wa sallam) would stand up for prayer and recite the duaa of Istiftaah and then he would recite:
أَعُوذُ بِاللَّهِ السَّمِيعِ الْعَلِيمِ مِنَ الشَّيْطَانِ الرَّجِيمِ مِنْ هَمْزِهِ وَنَفْخِهِ وَنَفْثِهِ
Narrated Abu Sa'iid al-Khudri:
When the Messenger of Allah (sallallaahu alayhi wa sallam) got up to pray at night (for tahajjud prayer) he said the takbiir and then said: "Glory be to Thee, O Allah," and "Praise be to Thee" and "Blessed is Thy name," and Exalted is Thy greatness." and "There is no god but Thee." He then said: "There is no god but Allah" three times; he then said: "Allah is altogether great" three times: "I seek refuge in Allah, All-Hearing and All-Knowing from the accursed devil, from his evil suggestion (hamz), from his puffing up (nafkh), and from his spitting (nafth)" He then recited (the Qur'an).
[Sunan Abu Dawud Hadith No. 775]
أَعُوذُ بِاللَّهِ مِنَ الشَّيْطَانِ الرَّجِيمِ
The above wording occurs in the following Hadith:
Narrated Sulaiman bin Sarad:
Two men abused each other in front of the Prophet (sallallaahu alayhi wa sallam) while we were sitting with him. One of the two abused his companion furiously and his face became red. The Prophet (sallallaahu alayhi wa sallam) said, "I know a word (sentence) the saying of which will cause him to relax if this man says it. Only if he said, "I seek refuge with Allah from Satan, the outcast.' " So they said to that (furious) man, 'Don't you hear what the Prophet (sallallaahu alayhi wa sallam) is saying?" He said, "I am not mad."
[Sahih Al-Bukhaari Hadith No. 6115]
When is Ta'awwudh said in prayer?
Ta'awwudh is said during prayer after one has completed the duaa' of 'Istiftaah as the following Hadith clearly shows:
Narrated Abu Sa'iid al-Khudri:
When the Messenger of Allah (sallallaahu alayhi wa sallam) got up to pray at night (for tahajjud prayer) he said the takbiir and then said: "Glory be to Thee, O Allah," and "Praise be to Thee" and "Blessed is Thy name," and Exalted is Thy greatness." and "There is no god but Thee." He then said: "There is no god but Allah" three times; he then said: "Allah is altogether great" three times: "I seek refuge in Allah, All-Hearing and All-Knowing from the accursed devil, from his evil suggestion (hamz), from his puffing up (nafkh), and from his spitting (nafth)" He then recited (the Qur'an).
[Sunan Abu Dawud Hadith No. 775]
Is Ta'awwudh to be said in every Rak'ah?
Sheikh Al-'albaani was of the opinion that one is to recite ta'awwudh prior to commencing the recitation of the Qur'aan in every Rak'ah of prayer. He derived his evidence from the generality of the following Verse of the Qur'aan. [1]
So when you recite the Qur'an, [first] seek refuge in Allah from Satan, the expelled [from His mercy].
[Qur'aan 16:98]
وأما استحبابه في كل ركعة فقد ذكرنا أن الأصح في مذهبنا استحبابه في كل ركعة وبه قال ابن سيرين وقال عطاء والحسن والنخعي والثوري وأبو حنيفة يختص التعوذ بالركعة الأولى وأما استحبابه للمأموم فمذهبنا أنه يستحب له كما يستحب للإمام والمنفرد وقال الثوري وأبو حنيفة لا يتعوذ المأموم لأنه لا قراءة عليه عندهما
According to Imaam Al-Nawawi the correct position of the [Shaafi] Madhab is that it is recommended [mustahab] to recite ta'awwudh in every Rak'ah of prayer. Imaam Ibn Siiriin also held this opinion.
According to Imaam Abu Hanifah, Imaam Maalik, and Imaam Al-Thawri, ta'awwudh is only specific to the first Rak'ah of prayer. [2]
كان رسول الله صلى الله عليه وسلم إذا نهض من الركعة الثانية استفتح القراءة بـ الحمد لله رب العالمين ولم يسكت
It is mentioned in a Hadith in Sahih Muslim that the Prophet, when he used to get up from the second Rak'ah, he would begin the recitation with Al-hamdul illaaahi rabbil alaa miin. [3]
فالأحوط الاقتصار على ما وردت به السنة، وهو الاستعاذة قبل قراءة الركعة الأولى فقط
Imaam Al-Shawkaani is of the opinion that one does not have to recite ta'awwudh in every Rak'ah. According to him it is better to confine oneself to what has come in the Sunnah and that is saying ta'awwudh prior to the commencement of the recitation of the first Rak'ah only. [4]
ولا نزاع بينهم أن الاستفتاح لمجموع الصلاة، والاكتفاء باستعاذة واحدة أظهر للحديث الصحيح عن أبي هريرة
Ibn Al-Qayyim also holds this opinion. [5]
Reference(s):
[1] Tamaam Al-Minnah Volume 1 Page 176 – 177
[2] Al-Majmoo' Volume 3 Page 326
[3] Sahih Muslim Hadith No. 599
[4] Nail Al-'awtaar Volume 2 Page 230
[5] Zaad Al-Ma'aad Volume 1 Page 234