Is the supplication, "There is no god but Allah, as many times as there has been and as many times as there will be, and as many times as there are moments of stillness and as many times as there are moments of movement," established [in the Sunnah], and what is its reward, and is it permissible to supplicate with it?

There is no objection to reciting this dhikr (remembrance), but the reward associated with it and what the angels supposedly said have not been authentically established. Discussions about angels and rewards are matters of the unseen (ghayb) and should not be based on speculation. Al-Tabarani narrated a weak hadith about words that are equivalent to many acts of remembrance. In Sahih Muslim, the Prophet, peace and blessings be upon him, said to Juwayriyah words that equalled all that she had recited throughout the day: "Subhanallah wa bihamdihi, adada khalqihi, wa rida nafsihi, wa zinata arshihi, wa midada kalimatihi." (Glorified is Allah and praised be He, as many times as the number of His creations, as much as pleases Him, as much as the weight of His Throne, and as much as the ink of His words.)