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

اَللَّهُمَّ إِنِّي أَسْأَلُكَ بِأَنِّي أَشْهَدُ أَنَّكَ اَنْتَ اللَّهُ لَا إِلَهَ إِلَّا أَنْتَ الْأَحَدُ الصَّمَدُ الَّذِيْ لَمْ يَلِدْ وَلَمْ يُوْلَدْ وَلَمْ يَكُنْ لَهُ كُفُوًا أَحَدٌ

Allaahumma 'innee 'as'aluka bi 'anni 'ash-hadu 'annaka 'AntAllahu laa 'ilaaha 'illaa 'Antal-'Ahadus-Samadul-ladhee 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. The Prophet (ﷺ) said: 'By the One in Whose Hand is my soul, he called upon Allah by His greatest Name, which, if He is called by it, He responds, and if He is asked by it, He gives.'

Reference: Sahih (Albani). Abu Dawud: 1493