It was narrated that Anas bin Malik said:"I was sitting with the Messenger of Allah (ﷺ) and a man was standing and praying. When he bowed, prostrated and recited the tashahhud, he supplicated, and in his supplication he said: "Allahumma inni as'aluka bi-anna lakal-hamd, lailaha illa ant, al-mannanu badi'us-samawati wal-ard, ya dhal-jalali wal-ikram! Ya hayyu ya qayyum! Inni as'aluka. (O Allah, indeed I ask You since all praise is due to You, there is none worthy of worship but You, the Bestower, the Creator of the heavens and earth, O Possessor of majesty and honor, O Ever-living, O-Eternal, I ask of You.)' The Prophet (ﷺ) said: 'Do you know what he has supplicated with?' They said: "Allah (SWT) and His Messenger know best." He 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.'"
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا خَلَفُ بْنُ خَلِيفَةَ، عَنْ حَفْصِ بْنِ أَخِي، أَنَسٍ عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ كُنْتُ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم جَالِسًا - يَعْنِي - وَرَجُلٌ قَائِمٌ يُصَلِّي فَلَمَّا رَكَعَ وَسَجَدَ وَتَشَهَّدَ دَعَا فَقَالَ فِي دُعَائِهِ اللَّهُمَّ إِنِّي أَسْأَلُكَ بِأَنَّ لَكَ الْحَمْدَ لاَ إِلَهَ إِلاَّ أَنْتَ الْمَنَّانُ بَدِيعُ السَّمَوَاتِ وَالأَرْضِ يَا ذَا الْجَلاَلِ وَالإِكْرَامِ يَا حَىُّ يَا قَيُّومُ إِنِّي أَسْأَلُكَ . فَقَالَ النَّبِيُّ صلى الله عليه وسلم لأَصْحَابِهِ " تَدْرُونَ بِمَا دَعَا " . قَالُوا اللَّهُ وَرَسُولُهُ أَعْلَمُ . قَالَ " وَالَّذِي نَفْسِي بِيَدِهِ لَقَدْ دَعَا اللَّهَ بِاسْمِهِ الْعَظِيمِ الَّذِي إِذَا دُعِيَ بِهِ أَجَابَ وَإِذَا سُئِلَ بِهِ أَعْطَى " .
Nesai
The Book of Forgetfulness (In Prayer) • Hadith 1300