Narrated Ibn ‘Abbas (radhi Allaahu anhuma): The Prophet (صلّى الله عليه وسلّم) used to say,
أَعُوذُ بِعِزَّتِكَ الَّذِي لاَ إِلَهَ إِلاَّ أَنْتَ،
الَّذِي لاَ يَمُوتُ وَالْجِنُّ وَالإِنْسُ يَمُوتُونَ
A’oodhu bi izzatika alladhee laa ilaaha illa Anta,
alladhee laa yamootu wal jinnu wal insu yamootoon
“I seek refuge (with You) by Your Izzat (Honour, Power and Glory) Laa ilaaha illa Anta, (none has the right to be worshipped but You), Who does not die while the jinns and the human beings die.”
Sahih al-Bukhari 7383 (Book 97, Hadith 13)
Translated by Dr. Muhammad Muhsin Khan
Dua at the start of the prayer
It was narrated from ‘Aishah that when the Prophet (ﷺ) started Salat he would say:
سُبْحانَكَ اللَّهُمَّ وَبِحَمْدِكَ، وَتَبارَكَ اسْمُكَ، وَتَعَالَى جَدُّكَ، وَلاَ إِلَهَ غَيْرُكَ
Glory is to You O Allah, and praise. Blessed is Your Name and Exalted is Your Majesty. There is none worthy of worship but You.
Subhaanaka Allaahumma wa bihamdika, wa tabaarakasmuka, wa ta’aalaa jadduka, wa laa ‘ilaaha ghayruka.
Abu Dawud 775, Ibn Majah 806, An-Nasa’I 899, At-Tirmithi 283. See Al-Albani, Sahih At-Tirmithi 1/77 and Sahih Ibn Majah 1/135.
Translation Source: From the Book “Fortress of the Muslim” ,
Dr. Sa’eed bin Ali Al-Qahtani, Dar-us-Salam Publication
Listen to the Excellent Explanation of this important supplication by Dr. Saleh as Saleh (rahimahullaah) at the link : https://abdurrahman.org/2017/07/07/opening-dua-in-prayer-subhaanaka-allaahumma-wa-bihamdika-wa-tabaarakasmuka/
From Buraydah (رضي الله عنه) that Allaah’s Messenger (صلى الله عليه و سلم) heard a man saying:
Meaning: “O Allaah: I ask you by the fact that I bear witness that You are Allaah, none has the right to be worshipped except You: The Unique One, the perfect Lord and Master upon Whom all the creation depends. The One Who has no parent and no child, and there is none like Him.”
So he (صلى الله عليه و سلم) said: ‹You have asked Allaah by the name which is such that if He is asked by it He gives, and if He is supplicated to by it He responds.› 
 Saheeh: ‘Saheeh Abee Daawood’ 1493
[Translated by Aboo Talhah Daawood ibn Ronald Burbank rahimahullaah]
Posted from : www.alitisaambissunnah.wordpress.com
Allaahumma innee as-aluka annee ash-hadu annaka antAllaahu laa ilaaha illaa anta, al-ahadu as-samadu, alladhee lam yalid wa lam yoolad, wa lam yakullahu kufuwan ahad.