Jami` at-Tirmidhi 213
جامع الترمذي#213SahihAnas bin Malik narrated:"On the Night of Isra, fifty prayers were made obligatory upon the Prophet. Then it was decreased until it was made five. Then it was called out: 'O Muhammad! Indeed My Word does not change; these five prayers will be recorded for you as fifty
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih
In-book reference: 2:65