Hadith 4:200
Waki’ narrated to us, from al-Fadl ibn Dalham, from al-Hasan, who said: Umar said: "If two men are in doubt regarding the dawn, let them eat until they are certain."
حدثنا وكيع عن الفضل بن دلهم عن الحسن قال قال عمر إذا شك الرجلان في الفجر فليأكلا حتى يستيقنا