The Prophet (ﷺ) as saying: When the night approaches from this side and the day retreats on that side, and the sun sets - according to the version of Musaddad - he who fasts has reached the time to break it.
Sunan Abi Dawud Book 14, Hadith 39
← Previous Hadith The Prophet (ﷺ) said: When any of you hears the summons to prayer while he has a vessel in his hand, he should not lay it down till he fulfils his need.

Sunan Abi Dawud Book 14, Hadith 38 Next Hadith → We went along with the Messenger of Allah (ﷺ) while he was fasting. When the sun set, he said to Bilal: Bilal, come down and prepare barley beverage for us. He said: Messenger of Allah, would that you waited for the evening. He said: Come down and prepare barley beverage for us. He said: Messenger of Allah, the say still remains on you (i.e. there remains the brightness of the day). He said: Come down and prepare barley drink for us. So he came down and prepared barley drink. The Messenger of Allah (ﷺ) drank it and said: When you see that the night approaches from this side, he who fasts has reached the time to break it ; and he pointed to the east with his finger.

Sunan Abi Dawud Book 14, Hadith 40