Hadith 3443
Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates that the Prophet Muhammad (peace and blessings be upon him) said: "When you see the new moon (of Ramadan), start fasting, and when you see it (the new moon of Shawwal), celebrate Eid al-Fitr. If the sky is cloudy for you, then complete the count of thirty days."