Ibn Umar was asked about fasting on the Day of Arafah while at Arafah. He replied, "I performed the pilgrimage with the Prophet ﷺ and he did not fast it, with Abu Bakr and he did not fast it, with Umar and he did not fast it, and with Uthman and he did not fast it. As for me, I fast it, but I neither command others to do so nor forbid them from it."
سئل ابن عمر عن صوم يوم عرفة بعرفة، فقال: حججت مع النبي ﷺ فلم يصمه، ومع ابي بكر فلم يصمه، ومع عمر فلم يصمه، ومع عثمان فلم يصمه، وانا اصومه، ولا آمر به ولا انهي عنه.
Tirmidhi (751) narrated it through several routes from Sufyan bin Uyayna and Ismail bin Ibrahim, from Ibn Abu Najeeh, from his father, who said, "Ibn Umar was asked," and he related it. Darimi (1806) and Ibn Hibban (3604) both narrated it through the route of Ismail bin Ibrahim, who is known as Ibn Ulaya. Tirmidhi said, "A hasan hadith. This hadith has also been narrated from Ibn Abu Najeeh, from his father, from a man, from Ibn Umar. Abu Najeeh's name was Yasar."I say, its narrators are trustworthy. Ibn Abu Najeeh is Abdullah bin Abu Najeeh, and his father Abu Najeeh's name was Yasar Makki, and both of them are among the narrators found in the Sahih collections.As for what is narrated concerning Abdul-Rahman bin Abu Bakr, that he came in to see Ayesha on the Day of Arafah while she was fasting and water was being sprinkled on her, and Abdul-Rahman said to her, "Break your fast," and she replied, "I will break my fast," and she had heard the Messenger of Allah say, "Fasting on the day of Arafah atones for the year that precedes it," this contains a break in the chain. Ahmad (24970) narrated it from Affan, who said, Hammad bin Salama told us, who said, Ata Khurasani informed us, that Abdul-Rahman bin Abu Bakr came in to see Ayesha, and he related it. But Ata is Ibn Abu Muslim Khurasani, who did not hear from Ayesha, nor from Abdul-Rahman bin Abu Bakr, nor indeed from any of the companions at all. Haythami said in al-Majmu (1893), "Ahmad narrated it, and Ata did not hear from Ayesha, indeed Ibn Main said, 'I do not know of him meeting any of the companions of the Prophet,' though the rest of its narrators are found in the Sahih collections."On this subject there is also what is narrated from Abu Hurairah, "that the Prophet forbade fasting on the Day of Arafah while at Arafah." Abu Dawud (2440) and Ibn Majah (1732) and Ahmad (8031) narrated it, and Ibn Khuzayma (2101) and Hakim (1/434) graded it sahih, all of them through the route of Hawshab bin Aqeel, who said, Mahdi Hijri told me, from Ikrima, who said, "We were with Abu Hurairah in his house, and he told us that the Messenger of Allah forbade fasting on the day of Arafah while at Arafah." Hakim said, "Sahih according to the criterion of Bukhari."I say, this is a mistake on his part, for Hawshab bin Aqeel and his teacher Mahdi Hijri are not among Bukhari's narrators. However, Hawshab bin Aqeel is trustworthy, while his teacher Mahdi, who is Ibn Harb Abdi Hijri, was only deemed trustworthy by Ibn Hibban, and for that reason Hafiz said in al-Taqrib, "Acceptable," meaning if corroborated, and he was not corroborated, so his hadith is weak in strength.Ibn Main said, "I do not know him." Ibn Hazm said, "Unknown, not to be relied upon."It has been established in the Sahih that the Prophet did not fast on the Day of Arafah while at Arafah, but the prohibition itself has not been established from him. Perhaps Abu Hurairah inferred the non-fasting from the Prophet's practice, and this Mahdi mistakenly reported it from him as a prohibition stated by the Prophet himself, when Abu Hurairah did not intend that.Umar, commander of the faithful, used to go around on the Day of Arafah among the encampments of the pilgrims until the heat drove him to the tent of a group of people, where he was given barley drink to drink and he drank it. Abdul-Razzaq (7818) narrated it from Ibn Jurayj, who said, Ata informed me, that he heard Ubaydullah bin Umayr say, "Umar went around," and he related it.