Say three times:

سُبْحَانَ رَبِّيَ الأَعْلَى

Glory is to my Lord, the Most High.

Subhaana Rabbiyal-A 'laa.

Abu Dawud, Ibn Majah, An-Nasa'i, At-Tirmithi, and Ahmad. See also Al-Albani, Sahih At-Tirmithi 1/83.