The Reward for Glorifying, Praising, Declaring God’s Unity and His Greatness - Section 3 Mishkat al-Masabih 2321
Arabic hadith text
وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ:" أَلَا أَدُلُّكَ عَلَى كَلِمَةٍ مِنْ تَحْتِ الْعَرْشِ مِنْ كَنْزِ الْجَنَّةِ لَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللَّهِ يَقُولُ اللَّهُ تَعَالَى: أَسلَمَ عَبدِي واستسلم ". رَوَاهُمَا الْبَيْهَقِيّ فِي الدَّعْوَات الْكَبِير
Translation
He said that God’s messenger offered to guide him to a word from under the Throne which was part of the treasure of paradise, it being “There is no might and no power except in God.” He added that God most high says, "My servant has resigned and submitted himself to me."Baihaqi transmitted the two traditions in [Kitab] ad-Da’awat al-kabir.