Anas said, "I was with the Prophet, may Allah bless him and grant him peace, when a man made supplication, saying, 'O Originator of the heavens! O Living, Self-Subsistent! I ask of You.' He said, 'Do you know by what he has made supplication? By the One in whose hand my soul is, he has asked Allah by the Name that He answers when He is asked by it."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَلِيٌّ بْنِ خَلَفِ بْنِ خَلِيفَةَ قَالَ: حَدَّثَنِي حَفْصُ ابْنُ أَخِي أَنَسٍ، عَنْ أَنَسٍ: كُنْتُ مَعَ النَّبِيِّ صلى الله عليه وسلم، فَدَعَا رَجُلٌ فَقَالَ: يَا بَدِيعَ السَّمَاوَاتِ، يَا حَيُّ يَا قَيُّومُ، إِنِّي أَسْأَلُكَ. فَقَالَ: أَتَدْرُونَ بِمَا دَعَا؟ وَالَّذِي نَفْسِي بِيَدِهِ، دَعَا اللَّهَ بِاسْمِهِ الَّذِي إِذَا دُعِيَ بِهِ أَجَابَ.
sunnah.com