It is strongly recommended to fast 9 Dhul Hijjah, known as Yawm `Arafah. The Prophet Muhammad, peace and blessings of Allah be upon him, said of this day, “The fast on the Day of `Arafah in the sight of Allah is such that He expiates the sins that came before the year of sins that come after.” Collected by Imam Muslim in Al-Jami` us-Sahih.
The day immediately after is 10 Dhul Hijjah, also known as Yawm un-Nahr (eng. the Day of Sacrifice). This is the second of the two yearly Eids and it is called Eid ul-Adha (eng. the Eid of the Sacrifice) and lasts three days (the opposite of `Eid ul-Fitr which is only one day). This commemorates the willingness of the Prophet Ibrahim, peace be upon him, to dedicate everything to Allah, even his very own life and that of his son, the Prophet Isma`il, peace be upon him.
This has been mentioned in Surat us-Saffat (37), ayat 83-119, Surat ul-Baqarah (2), ayat 127-141 and a passing reference in Surat ul-Kawthar (108), ayah 3. Let us try to obtain the reward for the fasting on 9 Dhul Hijjah and also make du`aa for those on Hajj recounting all the events of the Prophet Ibrahim, peace be upon him, some 4,000 years ago.
We would like to leave you with a quote from Imam Musa Al-Qaddumi (d. 1336 AH), may Allah have mercy upon him, who said the following of the sacrifice done on 10 Dhul Hijjah in his Mukhtasar Dalil it-Talib, pp. 301-302:
The sacrifice of `Eid is an emphasised sunnah  and it is permissible to sacrifice a goat that is one year old. It is also valid to have the sheep sacrificed that is half a year old.It is allowed to sacrifice the cow as well as the buffalo that is two years old. You may sacrifice the camel that is five years old.  The time for slaughtering is after the`Eid prayer up until the end of the second day of Tashriq.