Sayyiduna Abu Hurayrah (may Allah be pleased with him) says: "The month is twenty-nine days, so do not fast until you see it, and do not break the fast until you see it. If it is clouded over for you, then complete the count of thirty. Your Eid al-Fitr is the day on which you break the fast, your Adha is the day on which you sacrifice, all of Arafat is a place of standing, all of Mina is a place of sacrifice, and every street of Makkah is a place of sacrifice."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8206
Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates that he (peace and blessings be upon him) said: "Fast upon sighting it." Then he narrated the hadith in the same way to the end, and he did not mention that the month is twenty-nine days.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8207
Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Your day of fasting is the day on which you fast, and your day of sacrifice is the day on which you sacrifice."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8208
Masruq (may Allah have mercy on him) says: I went to Sayyidah Aishah (may Allah be pleased with her) on the Day of Arafah, and she said: Give Masruq sawiq to drink and add plenty of sweetening to it. He says: I said: Nothing kept me from fasting today except that I feared it might be the Day of Sacrifice (Nahr). Sayyidah Aishah (may Allah be pleased with her) said: Nahr is the day on which the people sacrifice, and Fitr is the day on which the people break the fast.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8209