The Messenger of Allah (ﷺ) heard a man saying:

اَللَّهُمَّ إِنِّي أَسْأَلُكَ بِأَنِّي أَشْهَدُ أَنَّكَ أَّنْتَ اللَّهُ لَا إِلَهَ إِلَّا أَنْتَ الْأَحَدُ الصَّمَدُ اَلَّذِي لَمْ يَلِدْ وَلَمْ يُوْلَدْ وَلَمْ يَكُنْ لَّهُ كُفُوًا أَحَدٌ

Allaahumma 'innee 'as'aluka bi'anni 'ash-hadu 'annaka 'AntAllahu laa 'ilaaha 'illaa 'Antal-'Ahadus-Samadul-ladhi lam yalid wa lam yoolad wa lam yakun lahu kufuwan 'Ahad

O Allah, I ask You, by the fact that I bear witness that You are Allah. There is none worthy of worship but You, the Only God, Independent of creation, Who was not begotten and begets not, and none is equal to Him. Then the Prophet (ﷺ) said, “I swear by the One in whose hand is my soul! You have supplicated Allah using His Greatest Name, when asked with this name He gives, and when supplicated by this name he answers.

Reference: Sahih. Abu Dawud: 1493