The hadi is a sacrificial animal immolated in the name of Allah by the pilgrim. It is to be slaughtered in Al-Haram and distributed among the poor and the needy.
With regard to this issue, we would like to cite what Sheikh Sayyed Sabiq states in his well-known book, Fiqh As-Sunnah:
There is disagreement among scholars about the time of slaughtering. According to Ash-Shafi`i it should be done on the Day of Nahr, 10th of Dhul-Hijjah, and during the days of Tashreeq which are 11th, 12th, and 13th of Dhul-Hijjah in light of the Prophet’s words, “All the days of Tashreeq are days for slaughtering.” (Ahmad)
If one missed slaughtering during these days, then the animal may be slaughtered at a later time to make up for it.
Malik and Ahmad hold the view that regardless of whether the slaughtering of the animal is obligatory or a supererogatory act of worship, it must be done during the appointed days. The Hanafi school also holds the same view concerning a pilgrim performing Hajj Tamattu` or Hajj Qiran. Such a pilgrim must slaughter the animal during the appointed days of Tashreeq.
As opposed to this, a sacrifice in fulfillment of a vow, atonement of sins, and offered as a supererogatory act of worship may be offered any time throughout the year.
Abu Salmah ibn `Abdul Rahman and An-Nakh’i reported that the time for slaughtering is from the Day of Nahr to the end of Dhul-Hijjah.