Jami` at-Tirmidhi 688
جامع الترمذي#688SahihIbn Abbas narrated that :the Messenger of Allah said: "Do not fast before Ramadan. Fast with its sighting, and break fast with its sighting, and if it is obscured from you, then complete thirty days
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: 8:7