Jami` at-Tirmidhi 791
جامع الترمذي#791SahihAishah narrated:"When the Messenger of Allah wanted to perform I'tikaf, he would perform Fajr prayer and then he would enter his place of I'tikaf
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
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 8:110