From ‘Umar ibn al Khattaab radi Allaahu ‘anhu who said.
The Messenger of Allaah sall Allaahu ‘alaihi wa sallam said:
“When the night approaches from here,
and the day goes away from here,
then let the fasting person break his fast.”
The Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah commented:
The Ameer ul Mu’mineen (Chief of the Believers) ‘Umar ibn al Khattaab radi Allaahu ‘anhu informs that the Prophet sall Allaahu ‘alaihi wa sallam clarified the signs of the time at which the fasting person breaks his fast.
And they are three signs which are inseparable from each other:
• The approach of the night from the east
• The departure of the day from the west
• The setting of the sun.
And the foundation of these signs is the setting of the sun because with it enters the night, which Allaah the Most High has made the limit for completion of the fast.
However the night appearing clearly from the east and the departing of the day from the west are (also) a proof for it, and follow on from it.
(taken from Sh Uthaymeen’s explanation of ‘Umdat-ul-Ahkaam
translated by Nasser ibn Najam)