Sahih Muslim 2704
Sahih Muslim · Book 48: The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness · It Is Recommend To Lower One's Voice When Saying Remembrance, Except In The Cases Where It Is Commanded To Raise The Voice Such As The Talbiyah Etc. It Is Recommend To Say A Great Deal, "There Is No Power And No Strength Except With Allah"
Abu Musa Ash'ari reported that Allah's Messenger (ﷺ) said to him:
حَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ ، أَخْبَرَنَا النَّضْرُ بْنُ شُمَيْلٍ ، حَدَّثَنَا عُثْمَانُ، - وَهُوَ ابْنُ غِيَاثٍ - حَدَّثَنَا أَبُو عُثْمَانَ ، عَنْ أَبِي مُوسَى الأَشْعَرِيِّ ، قَالَ قَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم " أَلاَ أَدُلُّكَ عَلَى كَلِمَةٍ مِنْ كُنُوزِ الْجَنَّةِ - أَوْ قَالَ - عَلَى كَنْزٍ مِنْ كُنُوزِ الْجَنَّةِ " . فَقُلْتُ بَلَى . فَقَالَ " لاَ حَوْلَ وَلاَ قُوَّةَ إِلاَّ بِاللَّهِ " .
Should I not direct you to the words from the treasures of Paradise, or he said: Like a treasure from the treasures of Paradise? I said: Of course, do that. Thereupon he said:" There is no might and no power but that of Allah."