PROPHET MUHAMMAD (ﷺ) said:
Whoever has an animal to sacrifice, when the crescent (1st) moon of Dhul-Hijjah appears, let him not remove anything from from his hair or nails, until he has offered sacrifice.

Narrated 'Ata bin Yasar:
"I asked Abu Abyub [Al-Ansari] how the slaughtering was done during the time of the Messenger of Allah (ﷺ). He said: 'A man would sacrifice a sheep for himself and the people in his household. They would eat from it and feed others, until the people (later) would boast about it and it became as you see now."

PROPHET MUHAMMAD (ﷺ) said:
There are no days during which righteous deeds are more beloved to Allah than these days,” meaning the (first) ten days of Dhul- Hijjah.

► PROPHET MUHAMMAD (ﷺ) said:
There are no days that are greater before Allaah or in which good deeds are more beloved to Him, than these ten days, so recite a great deal of
1) Tahleel (Laa ILaaha IL LaL Laah),
2) Takbeer (Allahu Akbar) and
3) Tahmeed (AL Hamdulillah)
during them.

PROPHET MUHAMMAD (ﷺ) said:
There are no days during which righteous deeds are more beloved to Allah than these days,” meaning the (first) ten days of Dhul- Hijjah. They said: “O Messenger of Allah (ﷺ)! Not even Jihad in the cause of Allah?” He (ﷺ) said: “Not even Jihad in the cause of Allah, unless a man goes out with himself and his wealth and does not bring anything back."

PROPHET MUHAMMAD (ﷺ) said:
used to fast the first nine days of Dhul-Hijjah.

QURAN 85:1
By the sky containing great stars

QURAN 85:2
And [by] the promised Day (Day of Resurrection)

QURAN 85:3
And [by] the witness (Friday) and what is witnessed (Day of Arafah)

PROPHET MUHAMMAD (ﷺ) said:
1) Al-Yawmul-Maw'üd (the Promised Day) is the Day of Resurrection,
2) And Al-Yawmul-Mashhüd (the Attended Day) is the Day of 'Arafah,
3) And Ash-Shãhid (the witness) is Friday.

Narrated: Ibn ‘Abbaas
The Messenger of Allaah (ﷺ) said:
Allah took the covenant from the loins of Adam in Na’maan, i.e., ‘Arafaah. He (Allah) brought forth from his loins all his offspring and spread them before Him (Allah), then He (Allah) addressed them, and said: (QURAN 7:172-173)

QURAN 7:172
And [mention] when your Lord took from the children of Adam - from their loins - their descendants and made them testify of themselves, [saying to them], "Am I not your Lord?" They said, "Yes, we have testified." [This] - lest you should say on the day of Resurrection, "Indeed, we were of this unaware."

QURAN 7:173
Or [lest] you say, "It was only that our fathers associated [others in worship] with Allah before, and we were but descendants after them. Then would You destroy us for what the falsifiers have done?"

Narrated 'Umar bin Al-Khattab:
Once a Jew said to me, "O the chief of believers! There is a verse in your Holy Book Which is read by all of you (Muslims), and had it been revealed to us, we would have taken that day (on which it was revealed as a day of celebration." 'Umar bin Al-Khattab asked, "Which is that verse?" The Jew replied,
(QURAN 5:3)

(QURAN 5:3)
"This day I have perfected your religion For you, completed My favor upon you, And have chosen for you Islam as your religion."

'Umar replied,"No doubt, we know when and where this verse was revealed to the Prophet. It was Friday and the Prophet (ﷺ) was standing at 'Arafat (i.e. the Day of Hajj)"

PROPHET MUHAMMAD (ﷺ) said:
I seek from ALLAH that fasting on the Day of 'Arafa (9th Zul-Hijjah) may atone (remove) for the sins of the preceding and the coming year.

PROPHET MUHAMMAD (ﷺ) said:
The best of supplication is the supplication of the Day of `Arafah. And the best of what I and the Prophets before me have said is:

TRANSLATION:
None has the right to be worshipped but Allah, Alone, without partner, to Him belongs all that exists, and to Him belongs the Praise, and He is powerful over all things.

PROPHET MUHAMMAD (ﷺ) said:
There is no day when ALLAH sets free more slaves from the Fire than the day of Arafat. He draws near, then He boasts about them before the Angels and says: What do these people want?