Jami` at-Tirmidhi 2971
جامع الترمذي#2971SahihNarrated 'Adi bin Hatim:"I asked the Messenger of Allah (ﷺ) about the fast, he said: 'Until the white (light) thread of dawn appears distinct to you from the black thread (of night)'" - he said: "So I took two ropes, one white and the other black to look at them. So the Messenger of Allah (ﷺ) said to me" - it was something that Sufyan (a sub narrator) did not remember - so he said: "It is only the night and the day
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
In-book reference: 47:23