THE VIRTUES AND BLESSINGS OF THE 10 DAYS OF DHUL-HIJJAH.

Ibn 'Abbas says about the verse, "Remember Allah during the well known days," that it refers to the first ten days of Dhul-Hijjah. [Bukhari]
This season of worship brings many benefits, such as the opportunity to correct ones faults and make up for any shortcomings or anything that one might have missed. Every one of these special occasions involves some kind of worship through which the slaves may draw closer to Allah, and some kind of blessing though which Allah bestows His favor and mercy upon whomsoever He will. The happy person is the one who makes the most of these special months, days and hours and draws nearer to his Lord during these times through acts of worship; he will most likely be touched by the blessing of Allah and will feel the joy of knowing that he is safe from the flames of Hell. [Ibn Rajab, al-Lataif, p.8]

Ibn 'Abbas reports that the Messenger of Allah (ﷺ) said,
 "No good deeds done on other days are superior to those done on these days [meaning the ten days of Dhul-Hijjah]." The companions asked, "O Messenger of Allah, not even jihad in the way of Allah?" He said, "Not even jihad, except for the man who puts his life and wealth in danger [for Allah's sake] and returns with neither of them." [This is related by the group except Muslim and an-Nasa'i]
Ahmad and at-Tabarani record from Ibn 'Umar that the Messenger of Allah (ﷺ) said, 
"There is no day more honorable in Allah's sight and no acts more beloved therein to Allah than those in these ten days. So say tahlil (There is no deity worthy of worship but Allah: La ilaha ill Allah), takbir (Allah is the greatest: Allahu Akbar) and tahmid (All praise is due to Allah: alhumdulillah) a lot [on those days]." [Reported by Ahmad, 7/224; Ahmad Shakir stated it is Sahih]

Abu Hurairah relates that the Messenger of Allah (ﷺ) said,
 "There are no days more loved to Allah for you to worship Him therein than the ten days of Dhul Hijjah. Fasting any day during it is equivalent to fasting one year and to offer salatul tahajjud (late-night prayer) during one of its nights is like performing the late night prayer on the night of power. [i.e., Lailatul Qadr]." [This is related by at-Tirmidhi, Ibn Majah, and al-Baihaqi]
One of the wives of the Prophet, (ﷺ) said:
 "Allah’s Messenger used to fast the (first) nine days of Dhul Hijjah, the day of ‘Ashura’, and three days of each month. [Abi Dawud]
Fasting on all these days, however, is not a Wajib (compulsory), nor is it a constant Sunnah that the Messenger, peace be upon him, never dropped. ‘A’ishah said: 
"I never saw the Messenger, peace be upon him, fast the ten days." [Muslim]

Fasting Day of Arafat

The Day of ‘Arafah - The Best Day of the Whole Year

The day of ‘Arafah is the day when the pilgrims stand in worship on the Mountain of ‘Arafah.

"There is no day on which Allah frees people from the Fire as He does no the day of ‘Arafah. He comes close (to those standing on ‘Arafah) and then revels before His angels, saying: "What are these people seeking?" [Muslim]

Abu Qatadah reported that the Messenger of Allah (ﷺ) said,
"Fasting on the day of 'Arafah is an expiation for two years, the year preceding it and the year following it. Fasting the day of 'Ashura is an expiation for the year preceding it." [This is related by "the group," except for al-Bukhari and at-Tirmidhi]
"There are five things that the Messenger (ﷺ) never abandoned: fasting the day of 'Ashura, fasting the [first] 10 [days of Dhul-Hijjah], fasting 3 days of every month and praying two Rak'ah before the dawn prayer." [This is related by Ahmad and an-Nasa'i]

'Uqbah ibn 'Amr reported that the Messenger of Allah (ﷺ) said,
 "The day of 'Arafah, the day of sacrifice, and the days of Tashriq are 'ids for us--the people of Islam--and they are days of eating and drinking." [This is related by "the five," except for Ibn Majah. At-Tirmidhi grades it Sahih]
Abu Hurairah stated, 
"The Messenger of Allah (ﷺ) forbade fasting on the day of 'Arafah for one who is actually at 'Arafah." [This is related by Ahmad, Abu Dawud, an-Nasa'i, and Ibn Majah] ."

This was all a well practiced Sunnah of our Nabi (ﷺ) and the reward for practicing what he had practiced is immense. :

The Prophet (ﷺ) said:
 “Whoever revives an aspect of my Sunnah that is forgotten after my death, he will have a reward equivalent to that of the people who follow him, without it detracting in the least from their reward.” (Tirmidhi)

Assalamu alaykum warhmathullahi wabarakathuhu!