Compiled by Imam Yahya ibn Sharaf al-Nawawi
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))
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].