Riyad as-Salihin 1236
'Umar bin Al-Khattab (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said: "When the night approaches from this side (i.e., the east) and the day retreats from that side (i.e., west) and the sun sets, then it is time for a person observing Saum (fasting) to break his fast." [Al-Bukhari and Muslim] .
وعن عمر بن الخطاب، رضي الله عنه قال‏:‏ قال رسول الله صلى الله عليه وسلم‏:‏ ‏
"‏إذا أقبل الليل من ههنا وأدبر النهار من ههنا، وغربت الشمس، فقد أفطر الصائم‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏