كتاب الذكر والدعاء والتوبة والاستغفار
48  
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness
(13)
Chapter: 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"
(13)
باب اسْتِحْبَابِ خَفْضِ الصَّوْتِ بِالذِّكْرِ
Sahih Muslim 2704 c

Abu Musa reported that he (and his other companions) were climbing upon the hillock along with Allah's Messenger (ﷺ) and when any person climbed up, he pronounced (loudly):

" There is no god but Allah, Allah is the Greatest." Thereupon Allah's Apostle (ﷺ) said: Verily, you are not supplicating One Who is deaf or absent. He said: Abu Musa or Abdullah b Qais, should I not direct you to the words (which form) the treasure of Paradise? I said: Allah's Messenger, what are these? He said:" There is no might and no power but that of Allah."
حَدَّثَنَا أَبُو كَامِلٍ، فُضَيْلُ بْنُ حُسَيْنٍ حَدَّثَنَا يَزِيدُ، - يَعْنِي ابْنَ زُرَيْعٍ - حَدَّثَنَا التَّيْمِيُّ، عَنْ أَبِي عُثْمَانَ، عَنْ أَبِي مُوسَى، أَنَّهُمْ كَانُوا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَهُمْ يَصْعَدُونَ فِي ثَنِيَّةٍ - قَالَ - فَجَعَلَ رَجُلٌ كُلَّمَا عَلاَ ثَنِيَّةً نَادَى لاَ إِلَهَ إِلاَ اللَّهُ وَاللَّهُ أَكْبَرُ - قَالَ - فَقَالَ نَبِيُّ اللَّهِ صلى الله عليه وسلم ‏"‏ إِنَّكُمْ لاَ تُنَادُونَ أَصَمَّ وَلاَ غَائِبًا ‏"‏ ‏.‏ قَالَ فَقَالَ ‏"‏ يَا أَبَا مُوسَى - أَوْ يَا عَبْدَ اللَّهِ بْنَ قَيْسٍ - أَلاَ أَدُلُّكَ عَلَى كَلِمَةٍ مِنْ كَنْزِ الْجَنَّةِ ‏"‏ ‏.‏ قُلْتُ مَا هِيَ يَا رَسُولَ اللَّهِ قَالَ ‏"‏ لاَ حَوْلَ وَلاَ قُوَّةَ إِلاَّ بِاللَّهِ ‏"‏ ‏.‏
Reference : Sahih Muslim 2704c
In-book reference : Book 48, Hadith 58
USC-MSA web (English) reference : Book 35, Hadith 6528
  (deprecated numbering scheme)