Bukhari

Hadith Commentary:
In the era of ignorance (Jahiliyyah), all other people would stand (for wuquf) at Arafat, but the Quraysh used to say that they were the family and dependents of Allah (Ahl Allah wa ‘iyaluhu), and therefore, they would not go outside the Haram for the standing (wuquf).
The Messenger of Allah (sallallahu alayhi wa sallam) was also from among the Quraysh, yet he, along with all the Muslims, stood at Arafat without distinguishing between Quraysh and non-Quraysh.
Arafat is outside the Haram, so the narrator was astonished that a Qurayshi, and on that day, was at Arafat.
The word “Hums” is derived from “Hamasah.”
The people of Quraysh were called “Hums” because they practiced strictness (hamasah) in their religion.

Hadith Commentary:
(1)
"Hums" is derived from "hamaasat," which means severity or strictness. The reason the Quraysh were called "Hums" was that they practiced strictness in their religion. Due to this strictness, they would not go beyond the boundaries of the Haram. Hazrat Jubayr bin Mut'im radi Allahu anhu was astonished because he saw the Messenger of Allah sallallahu alayhi wa sallam standing outside the boundaries of the Haram in the plain of Arafat during Hajj. The purpose of the Messenger of Allah sallallahu alayhi wa sallam was to abolish this innovation of the Quraysh through his own action.

(2)
Hazrat Jubayr bin Mut'im radi Allahu anhu narrates that the Quraysh would return from Muzdalifah. They used to say that, because we are Hums, we cannot go outside the boundaries of the Haram, and thus, on the occasion of Hajj, they had abandoned the standing at Arafat. However, I saw the Messenger of Allah sallallahu alayhi wa sallam during the era of ignorance standing with the people in the plain of Arafat on a mount, then he came with the people to Muzdalifah, stood there, and returned with the people from there. In one narration, it is mentioned that the Messenger of Allah sallallahu alayhi wa sallam did so by the guidance and command of Allah. (Fath al-Bari: 3/652)

(3)
On one occasion, the Messenger of Allah sallallahu alayhi wa sallam said: "The best supplication is the supplication of the Day of Arafah. And the best words that I and the Prophets before me have said are: (La ilaha illallahu wahdahu la sharika lahu, lahu'l-mulku wa lahu'l-hamdu wa huwa 'ala kulli shay'in qadir)." (Jami' al-Tirmidhi, al-Da'awat, Hadith: 3585)

(4)
It should be noted that on the Day of Arafah, it is recommended (mustahabb) to stand near Jabal Rahmah after the Zuhr and Asr prayers and make supplications. Besides this, one can stand at any place in the plain of Arafat. The Messenger of Allah sallallahu alayhi wa sallam said: "I am standing here, but the entire plain of Arafat is a place for standing (wuquf)." (Sahih Muslim, al-Hajj, Hadith: 2952(1218))