Abd al-Aziz bin Abdullah bin Khalid bin Asid (may Allah have mercy on him) says that the Messenger of Allah (peace and blessings be upon him) said: "The Day of Arafah is the day on which the people stand at Arafah."
This is a good mursal report.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9828
Hadith Gradingمحدثین:ضعيف
Hadith Takhrij«ضعيف۔ اخرجه ابوداود في المراسيل 138»