Silsilat al-Ahadith al-Sahihah

Sayyiduna Abu Umamah Sadi bin ‘Ajlan Bahili (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: “Shall I not tell you of a remembrance better than the continuous remembrance of night and day? Then remember in this way: I declare the purity of Allah as many times as the number of His creation. I declare the purity of Allah as much as would fill His creation. I declare the purity of Allah as many times as the number of things in the earth and the heavens. I declare the purity of Allah as much as would fill what is in the earth and the heavens. I declare the purity of Allah as much as would fill His creation. I declare the purity of Allah as many times as the number of things He has counted in His Book, and I declare the purity of Allah as much as would fill everything. Then you should say «اَلْحَمْدُ لِلّٰهِ» in the same way (i.e., in the supplication, replace «سبحان الله» with «اَلْحَمْدُ لِلّٰهِ» and complete the supplication).”