It is narrated from Sayyiduna Umar (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When the night comes from here and the day departs from there, then the fasting person should break his fast; by this is meant the east and the west."
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 192