Sunan At-Tirmidhi

Narrated '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