When the Messenger of Allah ﷺ began the prayer, he would say, "Glory be to You, Allah, and praise be to You. Blessed is Your name, exalted is Your majesty, and there is no god but You."
حدثنا حسين بن عيسى حدثنا طلق بن غنام حدثنا عبد السلام بن حرب الملائي عن بديل بن ميسرة عن أبي الجوزاء
كان رسول الله ﷺ إذا استفتح الصلاة قال سبحانك اللهم وبحمدك وتبارك اسمك وتعالى جدك ولا إله غيرك
[Sahih] Daraqutni narrated it, 1/299, from the hadith of Husayn bin Isa, through him. Hakim, 1/35. Its basis is found in Muslim, see the following hadith, 783, and the preceding hadith serves as a corroborating witness for it. (Mujam 120, 121) — Chapter on the pause after opening [the prayer] (Tuhfah 124)