In the Name of Allah, the Most Gracious, the Most Merciful

1- Doing good deeds on those days is better than doing them on other days: ‎‎‎‎‎it was narrated on the authority of Ibn ‘Abbaas that the Prophet said:‎‎‎‎‎ ‎‎‎‎“No good deeds done on other days are superior to those done on these days (meaning the first ten days of Thul-Hijjah).”Then some companions of the Prophet said, ”Not even Jihaad ?” He replied: “Not even Jihaad, except that of a man who puts himself and his property in danger (for the Sake of Allaah) and does not return with any of those things.” [Al-Bukhaari and Muslim]‎‎‎‎.

2- It was reported that the Prophet(PBUH) used to observe fasting in those days: One of the Prophet`s wives said: “ The Messenger of Allah used to fast nine days of Thul-Hijja, the Day of Ashora`, and three days of every month-Mondays and Thursdays.”{Abu Dawood}.      

3- ‎‎‎‎Allah, The Almighty, Says (what means):‎‎‎‎‎ {‎By the dawn And [by] ten nights}  [Quran 89:1, 2] . The ten nights are the ten days of Thul-Hijjah‎‎‎‎. Allah, The Almighty, swore by these days and He only swears by whatever is exalted and lofty in stature. 

4- Allah, The Almighty, says: “ and celebrate the name of God, through the Days appointed, over the cattle which He has provided for them (for sacrifice).”{Al-Hajj/28}.The Days appointed are the first ten days of Thul-Hijjah as stated by scholars of Tafseer (exegesis).

5- The Prophet(PBUH) said that these days are the best days in life: Jabir(May Allah be pleased with him) reported that the Prophet(PBUH) said: “ The best days of this life are the ten days- the ten days of Thul-Hijja. The companions said: aren`t there days spent for Allah`s sake better than them ?he said: there aren`t, except for a man who goes out for Jihaad . “ {Albazzar& Al-Monziri}

6-‎These days have the Day of ‘Arafah, (the Day of major Hajj )which is the ninth day of Thul-Hijjah.‎ The virtues of this Day are great and innumerable. It was reported that the Prophet(PBUH) urged Muslims-non-pilgrims- to observe fasting on this great Day. He said: "Fasting the Day of Arafah atones the sins committed a year before  it and those which will be committed a year after it."{Muslim}.

7-‎These days have the Day of Nahr (sacrifice) which is the tenth day of Thul-Hijjah, the Day of Eid. This is the best day as stated in the following Hadeeth:‎ ‎‎‎‎"The best of days in the sight of Allah, The Almighty, is the Day of Nahr, then the Day of Qurr( the first day of Tashreeq)." [Ahmad, Abu Daawood: Saheeh chain of narrators]‎‎‎‎.