Sunan an-Nasa'i — The Book of Salah — Hadith No: 449
Translation
Anas bin Malik and Ibn Hazm said:"The Messenger of Allah (ﷺ) said: 'Allah, the Mighty and Sublime, enjoined fifty prayers upon my Ummah, and I came back with that until I passed by Musa, peace be upon him, who said: 'What has your Lord enjoined upon your Ummah?' I said: 'He has enjoined fifty prayers on them.' Musa said to me: 'Go back to your Lord, the Mighty and Sublime, for your Ummah will not be able to do that.' So I went back to my Lord, the Mighty and Sublime, and He reduced a portion of it. Then I came back to Musa and told him, and he said: 'Go back to you Lord, for your Ummah will not be able to do that.' So I went back to my Lord, the Mighty and Sublime, and He said: 'They are five (prayers) but they are fifty (in reward), and the Word that comes from Me cannot be changed.' [1] I came back to Musa and he said: 'Go back to your Lord.' I said: 'I feel too shy before my Lord, the Mighty and Sublime.'" [1]See Surah Qaf 50: