Sahih Muslim | Book 6 | Hadith Number 2421

Narrated by 'Umar (Allah be pleased with him)
'Umar (Allah be pleased with him) reported Allah's Messenger (may peace be upon him) as saying: When the night approaches and the day retreats and the sun sinks down, then the observer of the fast should break it. Ibn Numair made no mention of the word "then".