The tenth of Dhul-Hijjah is `Eid ul- Ad-ha or the day of an-Nahr (slaughtering). It marks the conclusion of the major rites of Hajj, and commemorates Allah's bounty on His Messenger Ibraheem, when He gave him a ram to sacrifice as ransom for his son Ismaa`eel, (peace be upon them both).
"The day of al-Fitr [i.e. `Eid ul-Fitr], the day of an-Nahr, and the days of Tashreeq are `Eid days for us Muslims. They are days of eating and drinking." [Ahmad, an-Nasaa'ee, Saheeh ul-Jaami` #8192]