PROPHET MUHAMMAD (ﷺ) said:
Fasting on the day of Arafah, I ask Allah that it may expiate for (the sins of) the year that comes before it, and the year that comes after it.

Narrated: Abü Qatâdah Al-Ansâri
He (Prophet Muhammad ﷺ) was asked about fasting on the Day of 'Arafah. He (ﷺ) said: "It expiates for the past and coming years."

PROPHET MUHAMMAD (ﷺ) said:
The Day of Arafah, the Day of Nahr, and the Days of Tashriq are Eid for us. The people of Islam, and they are days of eating and drinking.

Ibn Abi Najib narrated from his father who said:
"Ibn Umar was asked about fasting (the Day of) Arafah (at Arafat). He said: 'I performed Hajj with the Prophet (ﷺ), and he did not fast it, and with Abu Bakr, and he did not fast it, and with Umar, and he did not fast it, and with Uthman, and he did not fast it. I do no fast it, nor order it nor forbid it."

Narrated Um Al-Fadl bint Al-Harith:
"While the people were with me on the day of `Arafat they differed as to whether the Prophet (ﷺ) was fasting or not; some said that he was fasting while others said that he was not fasting. So, I sent to him a bowl full of milk while he was riding over his camel and he drank it."