Volume 2, Book 15, Number 772:
The Prophet said, “Whoever slaughtered (his sacrifice) before the ‘Id prayer, should slaughter again.” A man stood up and said, “This is the day on which one has desire for meat,” and he mentioned something about his neighbors. It seemed that the Prophet believed him. Then the same man added, “I have a young she-goat which is dearer to me than the meat of two sheep.” The Prophet permitted him to slaughter it as a sacrifice. I do not know whether that permission was valid only for him or for others as well.
Next Hadith will explain the incident better..
Volume 2, Book 15, Number 773:
Narrated Al-Bara’ bin ‘Azib:
The Prophet delivered the Khutba after offering the prayer on the Day of Nahr and said, “Whoever offers the prayer like us and slaughters like us then his Nusuk (sacrifice) will be accepted by Allah. And whoever slaughters his sacrifice before the ‘Id prayer then he has not done the sacrifice.” Abi Burda bin Niyar, the uncle of Al-Bara’ said, “O Allah’s Apostle! I have slaughtered my sheep before the ‘Id prayer and I thought today as a day of eating and drinking (not alcoholic drinks), and I liked that my sheep should be the first to be slaughtered in my house. So slaughtered my sheep and took my food before coming for the prayer.” The Prophet said, “The sheep which you have slaughtered is just mutton (not a Nusuk).” He (Abu Burda) said, “O Allah’s Apostle! I have a young she-goat which is dearer to me than two sheep. Will that be sufficient as a Nusuk on my behalf? “The Prophet (p.b.u.h) said, “Yes, it will be sufficient for you but it will not be sufficient (as a Nusuk) for anyone else after you.”
Don’t eat anything before Eid prayer on Eid-ul-Adha (if you’re offering the sacrifice on the first day). But it is Sunnah to eat dates in an odd number on Eid-ul-Fitr.
..But on Eid al-Adha it is mustahabb not to eat anything until one comes back from the prayer, so he should eat from the udhiyah if he has offered a sacrifice. If he is not going to offer a sacrifice there is nothing wrong with eating before the prayer.
Eid al-Adhaa is the tenth day of Dhoo’l-Hijjah, the last (twelfth) month of the Hijri or Islamic calendar. It is, as the Prophet (peace be upon him) said: “The greatest day in the sight of Allaah, may He be blessed and exalted, the Day of Sacrifice . . .” (Reported by Abu Dawud; see also Saheeh al-Jaami‘, 1064).
It is also the greatest day of Hajj, as the Prophet (peace be upon him) told us. (Reported by al-Tirmidhi, see Saheeh al-Jaami‘, 8191).
The reason why it is described as the greatest day of the year is that it combines so many acts of worship which are not combined on any other day, such as the Eid prayer, offering the sacrifice, reciting Takbeer (glorifying Allaah), and widespread remembrance of Allaah. For the pilgrims in Makkah, it also includes offering a sacrifice, stoning the pillars representing Shaytaan (the devil), shaving the head (for men only; women merely cut a little off their hair), and performing Tawaaf (circumambulation of the Ka‘bah) and Sa‘ee (running between the two hills of Safaa and Marwa).
Why sacrifice? We all know the story of Ibrahim (AS), but do we really know the spirit of sacrifice? Is it just the meat we eat and distribute among family, friends, neighbors and the poor, or is there something more to it? Here’s one unbelievably awesome video that should explain it all: