Bukhari

Hadith Commentary:
The correspondence between the hadith and the chapter is evident. Sufyan ibn ‘Uyaynah, who also appears in the chain of narration here, was born in the month of Sha‘ban in 107 AH in Kufa.
He was an imam, a scholar, an ascetic, and a pious man. All the hadith scholars placed their trust in him.
It is their unanimous statement that if it were not for Imam Malik and Sufyan ibn ‘Uyaynah, the knowledge of Hijaz would have perished.
He passed away in Makkah Mukarramah on the first of Rajab in 198 AH and was buried in Hajun. He performed seventy Hajj pilgrimages.
Rahimahum Allah ajma‘in (Ameen).

Hadith Commentary: Benefits and Issues: When darkness appears in the east, and the light in the west disappears, and the sun sets, this is a sign that the time of fasting has been completed and now, according to the Shariah, the fast has ended.
Because the day in which the fast was to be observed has come to an end, there is no longer any time left to continue the fast.
Therefore, the fasting person should break the fast; he should not, out of excessiveness or extremism, unnecessarily and without reason, continue the fast when its time has already ended.

1:
“One meaning of ‘You have broken your fast’ is that the time for you to break your fast has arrived.
And the second meaning is that, according to the Shari‘ah, you have become one who breaks the fast, even if you have not yet eaten or drunk anything, because as soon as the sun sets, the fast comes to its end. In this, the time for fasting has been specified: it is from true dawn (subh sadiq) until sunset.”