Kuraib reports: Lady Umm al-Fadl bint al-Harith (may Allah be pleased with her) sent me to the service of Sayyiduna Muawiyah (may Allah be pleased with him). He says: I came to Syria, fulfilled the task of Umm al-Fadl, and during that time the crescent of Ramadan was sighted. I was present in Syria; I saw the crescent on the night of Friday. Then, at the end of the month, I came to Madinah Munawwarah. Sayyiduna Abdullah ibn Abbas (may Allah be pleased with them both) spoke with me, and when I mentioned the sighting of the crescent, he asked: When did you see the crescent? I replied: I saw it on the night of Friday. Sayyiduna Abdullah ibn Abbas (may Allah be pleased with them both) asked: Did you see it yourself? I said: Yes! And the people also saw it, and I fasted, and Sayyiduna Muawiyah (may Allah be pleased with him) also fasted. Sayyiduna Abdullah ibn Abbas (may Allah be pleased with them both) said: "We saw it on the night of Saturday, and we will continue to fast until we complete thirty days or see the crescent of Shawwal." So I said to him: Is the sighting of the crescent and fasting of Sayyiduna Muawiyah (may Allah be pleased with him) not sufficient for you? He replied: No! The Noble Prophet (peace and blessings be upon him) has given us this instruction. This narration is authentic.

Sayyiduna Abu Mas’ud Ansari (may Allah be pleased with him) narrates: (In the month of Ramadan) on the morning of the thirtieth day, two villagers came and testified before the Prophet Muhammad (peace be upon him) that they had seen the moon the previous night. The Prophet Muhammad (peace be upon him) ordered the people:“Break your fast and celebrate Eid al-Fitr.”
Chapter: Making the intention (for fasting) at night itself.