Jami At Tirmidhi
213
Sahih+3

Anas 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

SahihAhmad Muhammad Shakir
SahihAl-Albani