Urwa reported,
The Arabs used to circle the Kaaba naked, except for the Hums. The Hums were Quraysh and their descendants. They would perform tawaf naked unless the Hums provided them with clothing. Men would give clothing to men, and women to women. The Hums did not leave Muzdalifa, while all other people would proceed all the way to Arafat.Hisham said, My father related to me from Ayesha 
that she said, "The Hums are the ones concerning whom Allah revealed to you, 'Then depart from where the people depart' [Baqarah 2:199]."She said, "The people used to depart from Arafat, while the Hums would depart from Muzdalifa, saying, 'We will only depart from within the sacred precinct.' When the verse 'Depart from where the people depart' was revealed, they returned to departing from Arafat."
Azami 5093
Sahihعن عروة قال
كانت العرب تطوف بالبيت عراة إلا الحمس- والحمس قريش وما ولدت-كانوا يطوفون عراة إلا أن تعطيهم الحمس ثيابا فيعطي الرجال الرجال والنساء النساء، وكانت الحمس لا يخرجون من المزدلفة وكان الناس كلهم يبلغون عرفات. قال هشام: فحدثني أبي عن عائشة رضي الله عنها قالت: الحمس هم الذين أنزل الله لك فيهم: {ثم أفيضوا من حيث أفاض الناس}. قالت: كان الناس يفيضون من عرفات، وكان الحمس يفيضون من المزدلفة يقولون لا نفيض إلا من الحرم، فلما نزلت: {أفيضوا من حيث أفاض الناس}: رجعوا إلى عرفات.
Bukhari narrated it in the Hajj chapter (1665) from the hadith of Ali bin Mushir, and Muslim narrated it in the Hajj chapter (1219:152) from the hadith of Usama. Both of them narrated from Hisham, from his father, and mentioned it, with the wording being that of Muslim. The wording of Bukhari is close to it, and in it, "So they pushed on to Arafat." That is, they were commanded to head toward Arafat to stand there and then move on from it. The tafsir of the verse will come later.Al-Hums is spelled with the ha vowelled with damma, followed by a silent meem, then a sin. Its meaning, as Ibrahim Harbi related in Ghareeb al-Hadith through the route of Ibn Jurayj, from Mujahid, who said, "Al-Hums are Quraysh and whoever among the tribes followed the same approach as Quraysh, such as the Aws, the Khazraj, Khuza, Thaqif, Ghazwan, Banu Amir, Banu Sasaa, and Banu Bakr. In the speech of the Arabs, al-ahmas means the harsh or severe one, and they were named this because of the strictness they imposed on themselves. When they entered the state of ihram for Hajj or Umrah, they would not eat meat, nor beat wool, nor beat hair. And when they arrived at Makkah, they would remove the clothes they had been wearing."Ibrahim also related, through the route of Abdul-Aziz bin Imran Madani, who said, "They were named Hums after the Kaaba, because it is ahmas, its stone being white shading toward black." Abu Ubayda Muammar bin Muthanna said, "Tahammasa means to become strict or harsh, and from this comes the expression 'the fierceness of battle intensified' when it grows severe."