Sahih Muslim 2704 c
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 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 Messenger (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 (ﷺ) , what are these? He said:" There is no might and no power but that of Allah."