Prayers and Meditations — Paragraph 310
Source (Arabic)
أَنْتَ ذُو القُدْرَةِ العَظِيمِ وَذُو البَطْشِ الشَّدِيدِ لا إِلهَ إِلاَّ أَنْتَ المُقْتَدِرُ القَدِيرُ.
Translation
Thou art, verily, the One Whose power is immense, Whose vengeance is terrible. No God is there beside Thee, the Almighty, the Most Powerful.