Mus'ab bin Sa'd narrates from his father that the Prophet Muhammad (peace be upon him) said: "Can any person not do this, that he earns one thousand good deeds every day?" So one of those sitting with the Prophet (peace be upon him) asked: How can a person earn one thousand good deeds every day? The Prophet (peace be upon him) replied: "He should recite Subhan Allah one hundred times, and recite Allahu Akbar one hundred times, and this will become one thousand good deeds."
Hadith Referenceمسند الحميدي / 80
Hadith Gradingمحدثین:إسناده صحيح
Hadith Takhrij« إسناده صحيح ، وأخرجه مسلم 2698، وأخرجه أبو يعلى الموصلي فى ”مسنده“:723، وفي صحيح ابن حبان: 825، وأحمد: 374/1 برقم: 1514»
Benefit: In this hadith, the virtue of saying "Subhan Allah" and "Allahu Akbar" is being mentioned. From this hadith, it is understood that by saying "Subhan Allah" one hundred times or "Allahu Akbar" one hundred times, one receives a thousand good deeds. It is narrated from Sayyiduna Abu Malik Ash'ari radi Allahu anhu that the Messenger of Allah sallallahu alayhi wa sallam said: Purity is half of faith, and "Alhamdulillah" fills the scale, and saying "Subhan Allah walhamdulillah" fills the scale, or he said: fills what is between the heavens and the earth. (Sahih Muslim: 223)
In the explanation of this hadith, the Qur'an commentator Hafiz Salahuddin Yusuf rahimahullah writes: Also, the virtues and reward of the aforementioned remembrances (adhkar) are mentioned, that if these words were given a physical form, the scale would fill the distance between the heavens and the earth. This, in fact, is a description of the vastness of Allah Ta'ala's grace and bounty and His boundless mercy. (Riyadh as-Salihin: 2/342)
Source: Musnad al-Humaydi: Commentary by Muhammad Ibrahim bin Bashir, Page: 80