Sayyiduna Abu Wa'il (may Allah be pleased with him) says: The letter of Sayyiduna Umar (may Allah be pleased with him) came to us while we were at Khaniqin: "The new moons, some of them are bigger than others; so when you see the new moon in the daytime, do not break your fast until evening comes, unless two Muslim men testify that they sighted it the previous evening."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7982
Mu'ammal bin Isma'il narrates from Sufyan (may Allah have mercy on him), and he added these words: "When you see the new moon at the beginning of the day, do not break your fast until two upright men testify that they sighted it the previous evening."
Abu Bakr (al-Naysaburi) said: If Mu'ammal has preserved it, then it is gharib (unusual); the imam Abd al-Rahman bin Mahdi contradicted him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7983
Abu Wa'il (may Allah have mercy on him) says: The letter of Sayyiduna Umar (may Allah be pleased with him) came to us at Khaniqin: the new moon is bigger in some cases than in others, so when you see the new moon at the beginning of the day, do not break your fast until two witnesses testify that they saw it the previous day.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7984
Shibak narrates from Ibrahim that he said: Sayyiduna Umar (may Allah be pleased with him) wrote to Utbah bin Farqad: "When you see the new moon in the daytime before the sun passes the meridian, on the completion of thirty days, then break your fast; and when you see it after the sun has passed the meridian, then do not break your fast, and remain fasting."
Ibrahim al-Nakha'i narrated it munqati' (with a broken chain), and the hadith of Abu Wa'il is more authentic than it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7985
Sayyiduna Salim bin Abdullah (may Allah have mercy on him) says that the people saw the new moon of Eid al-Fitr in the daytime, so Abdullah bin Umar (may Allah be pleased with him) completed his fast until night, and said: "No, not until it is seen from where it is seen at night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7986
Salim (may Allah have mercy on him) says that Sayyiduna Ibn Umar (may Allah be pleased with him) used to say: When people see the new moon in the daytime they break their fast; it is not right for you to break your fast until you see it at night from where it is seen.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7987