Mishkat al-Masabih 7 Fasting كتاب الصوم 29

وَعَنْ عُمَرَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِذَا أَقْبَلَ اللَّيْل من هَهُنَا وَأدبر النَّهَار من هَهُنَا وَغَرَبَتِ الشَّمْسُ فَقَدْ أَفْطَرَ الصَّائِمُ»

‘Umar reported God’s messenger as saying, “When the night approaches on this side and the day retreats on that side and the sun sets, he who fasts has reached the time to break it.” (Bukhari and Muslim.)