Say three times:

سُبْحَانَ رَبِّيَ الْعَظِيمِ

Glory to my Lord the Exalted

Subhaana Rabbiyal-'Adheem.

Abu Dawud 870, Ibn Majah 897, An-Nasa'I 1107, At-Tirmithi 262, and Ahmad 3514. See Al-Albani's Sahih At-Tirmithi 1/83.