I came to Anas bin Malik at the time of Asr on a day when people were uncertain whether Ramadan had begun, intending only to greet him. He called for food and ate.I asked, "Is what you are doing a sunnah?"He replied, "Yes."
دخلت على أنس بن مالك عند العصر يوم يشكون فيه رمضان، وأنا أريد أن أسلم عليه، فدعا بطعام فأكل. فقلت: هذا الذي تصنع سنة؟ قال: نعم.
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Tabarani narrated it in Al-Awsat (9039) through Muhammad bin Jafar bin Abu Kathir, from Zayd bin Aslam, from Muhammad bin Munkadir, from Muhammad bin Kaab Qurazi, and he mentioned it. Haythami said in Al-Majmu (3/148), "Its narrators are the narrators of the sahih." I say, it is as he said. As for Muhammad bin Jafar bin Abu Kathir, even though he alone transmitted it from Zayd bin Aslam, as Tabarani said, he is a reliable and firmly established narrator, and being the sole transmitter does not harm his reliability.Among those from whom the prohibition of fasting on the day of doubt has been reported are Umar, Ali, Abdullah bin Masud, Abdullah bin Abbas, Ibn Umar, Huzaifa, Anas bin Malik, and others. Ibn Abu Shayba mentioned them (713, 712), as did Bayhaqi in Sunan al-Kubra (4/209–210). This was also the view of Sufyan Thawri, Malik bin Anas, Abdullah bin Mubarak, Shafii, Ahmad, and Ishaq. These scholars disliked that a man should fast on the day about which there is doubt. See Tirmidhi (3/61).Ayesha and Asma, the two daughters of Abu Bakr, used to fast on the day of doubt, and Ayesha would say, "That I should fast a day of Shaban is dearer to me than that I should break a day of Ramadan."Ibn Umar used to say, "If the crescent of Ramadan is not sighted on the night of the thirtieth of Shaban, and the sky was clear, then there is no fasting for Ramadan. But if it was not clear, and there was cloud in the sky, the people would begin the morning fasting, and it would count for them as Ramadan, if it were later established that the month had been twenty-nine days." There is nothing in his statement indicating fasting on the day of doubt. It has been firmly established from him that he said, "Even if I fasted the whole year, I would still break my fast on the day about which there is doubt." Ibn Abu Shayba narrated this (713) from Waki, from Sufyan, from Abdul-Aziz bin Hakeem, who said, I heard Ibn Umar, and then he mentioned it.The majority of scholars said that if the news came after that day, or after the people had entered the evening, or if they had erred in their estimation of the crescent, they would be required to make up that day.