Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.113.

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 Zhul-Hijjah, and during Ayyam at-Tashriq (the 11th, 12th or 13th of Zhul-Hijjah) in light of the Prophet’s words “All the Tashriq days (l0th, 12th and 13th of Zhul-Hijjah) are Days for Slaughtering” as reported by Ahmad.

If one missed slaughtering during these days, then one may slaughter an animal later on to make up for it.

Malik and Ahmad hold 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 (tashriq) days.

As opposed to this, a sacrifice in fulfilment of a vow, atonement of sins, and offered as a supererogatory act of worship may be offered any time during the year.

Abu Salmah bin Abdul Rahman and An-Nakh’i reported that the time for slaughtering is from the Day of Nahr to the end of Zhul-Hijjah.