This is a sunnah act.
Dawud :: Book 3 : Hadith 774
Narrated AbuSa’id al-Khudri:
When the Apostle of Allah (peace_be_upon_him) got up to pray at night (for tahajjud prayer) he uttered the takbir 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).
أعُوذُ بالله السّميع العَليم مِنَ الشّيطانِ الرّجيم مِنْ هَمْزِهِ وَنَفْخِهِ وَنَفْثِهِ
or we can also say al istiadhah.