Question: What are the virtues of the month of Dhu’l-Hijjah?
ANSWER
The month in which there is Eid al-Adha is called Dhu’l-Hijjah. The value of the acts of worship performed in the first 10 days of Dhu’l-Hijjah is great. It is stated in hadith-i sharifs:

(The fast observed on the first days of Dhu’l-Hijjah is equal to fasting the whole year. Spending a single night of it worshiping is like spending the Day of Qadr worshiping.) [Ibn Majah]

(For a deed done on the first 10 nights of Dhu’l-Hijjah is given 700 times as much thawab as of it.) [Bayhaqi]

(A Muslim who observes a fast on the Day of Tarwiya and who does not say anything sinful will enter Paradise.) [Ramuz]

(Whoever fasts on the first 9 days of Dhu’l-Hijjah is given thawab for each day as if he emancipated 100 slaves or as if he gave 100 horses to people who perform jihad or as if he sent 100 camels to Ka’ba for sacrifice.) [R. Nasihin]

(Shame on him who is destitute of the benefits of these 10 days. One should be fasting especially on the 9th [Arafa] day. It contains so many benefits that they are countless.) [T. Ghafilin]

(One who fasts on the first 9 days of Dhu’l-Hijjah is given thawab of a whole year for each day.) [Abul Barakat]

(The first 10 days of Dhu’l-Hijjah are equal to a thousand days in virtue. The Day of Arafa is equal to ten thousand days.) [Bayhaqi]

(There are no deeds more valuable than the ones done on the first 10 days of Dhu’l-Hijjah.) [Tabarani]

(In the sight of Allah there are no deeds more valuable than the ones done on the first 10 days of Dhu’l-Hijjah. During these days, say tasbih, tahmid, tahlil and takbir frequently.) [Tabarani]

Tasbih: Subhanallah
Tahmid: Alhamdulillah
Tahlil: La ilaha illallah
Takbir: Allahu akbar

When our Master the Prophet said that the deeds done on the first 10 days of Dhu’l-Hijjah were more valuable than the ones done in other months, the Blessed Companions asked, “O the Messenger of Allah, are they more valuable than even jihad in the way of Allah?” He answered, “Yes, they are more valuable than even jihad. However, the jihad of him who fights without sparing his life and wealth and then becomes a martyr is more valuable.” (Bukhari)

Hadrat Abud-darda said: “One should fast on the first 9 days of Dhu’l-Hijjah, give plenty of sadaqah, make du’a and seek forgiveness many times because the Messenger of Allah said, ‘Shame on him who is destitute of the benefits and barakah of these days.’ Whoever fasts on the first 9 days of Dhu’l-Hijjah, it brings barakah to one’s life, increases one’s wealth, and protects one’s family against calamities. One’s sins are forgiven, and one earns many times more thawab for one’s good deeds. One experiences an easy death, and one’s grave becomes luminous. One attains high grades in Paradise.” (Shir’a)

It is sunnat to clip one's hair, beard, and nails every week. Hadrat Ibn Abidin says, “These acts of sunnat should not be delayed during the first 10 days of the month of Dhu’l-Hijjah. The hadith-i sharif that states ‘The person who is to perform the qurban must not clip his hair or trim his nails when the month of Dhu’l-Hijjah begins!’ is not a command. It is mustahab to delay these acts until
after performing the qurban." For a person who will perform the qurban, it is mustahab not to cut his hair, beard, moustache or nails from the first day of the month of Dhu’l-Hijjah till after performing the
qurban. But it is not wajib. It will not be sinful for him to do these
acts, nor will it decrease the thawab for qurban.

If one visits an ill person during these days, one will be considered as if one asked after the friends of Allahu ta’ala and visited them. It brings much thawab to read a book of Ahl-i Sunnat scholars during these 10 days. It is fard for everyone, men or women, to learn our religion and the aqidah of Ahl-i Sunnat. It is our main duty to teach it to our children.

Question: Fasting and doing acts of worship on the first 9 days of Dhu’l-Hijjah bring thawab. Likewise, does doing acts of worship on the 10th and 11th days of it bring thawab?
ANSWER
Yes, it brings much thawab. The 10th day of Dhu’l-Hijjah is the first day of Eid al-Adha. It is stated in hadith-i sharifs:

(The doors of mercy open at 4 nights. Du’a and seeking forgiveness performed these days are not rejected. They are the first nights of Eid al-Fitr and Eid al-Adha, the Night of Barat, and the Night of Arafa.) [Isfahani]

(Whoever spends the nights of eids worshiping, his heart does not die on the day when hearts die.) [Ibn Majah]