سُبْحَانَكَ اللَّهُمَّ وَبِحَمْدِكَ، وَتَبَارَكَ اسْمُكَ، وَتَعَالَى جَدُّكَ، وَلَا إِلَٰهَ غَيْرُكَ
Subhanaka Allahumma wa bihamdika, wa tabarakasmuka, wa ta'ala jadduka, wa la ilaha ghayruk
Glory be to You, O Allah, and praise be to You. Blessed is Your Name, exalted is Your Majesty, and there is no deity worthy of worship except You.
Opening supplication (Thana) recited silently after Takbir al-Ihram
This dua glorifies Allah and is the recommended opening for prayer.