Praise be to Allaah.
The command to give the meat of the sacrifice in charity is reported in a number of ahaadeeth, as was the permission to eat some and preserve some.
Al-Bukhaari and Muslim reported that ‘Aa’ishah (may Allaah be pleased with her) said: “Some poor families among the people of the desert came to al-Madeenah on the occasion of ‘Eid al-Adhaa at the time of the Messenger of Allaah (peace and blessings of Allaah be upon him). The Messenger of Allaah (peace and blessings of Allaah be upon him) said, ‘Keep with you meat sufficient for three days, and whatever is left, give in charity.’ After that, they said, ‘O Messenger of Allaah, the people made water-skins with [the hides of] their sacrificial animals, and they rendered the fat from them. The Messenger of Allaah (peace and blessings of Allaah be upon him) said, ‘What about it?’ They said, ‘You forbade us to eat the meat of our sacrificial animals after three days.’ He said, ‘I forbade you to do that because of the people who came, but now eat some and preserve some and give some in charity.’”(Reported by Muslim, 3643).
Al-Nawawi said, commenting on this hadeeth: “ The phrase ‘I forbade you to do that because of the people who came’ refers to the poor Bedouin who came to Madeenah, and this was so that they could be helped. ‘Rendered’ means that they melted down the fat from the animals (to be stored and used).
The phrase ‘I forbade you to do that because of the people who came, but now eat some and preserve some and give some in charity’ is a clear statement that this prohibition of keeping more than three days’ worth of meat no longer applies; it is also a commandment to eat some and to give some in charity. With regard to the portion to be given in charity, if it is a voluntary sacrifice, then giving some of it in charity is obligatory, according to the view regarded by our companions as correct. It is preferable [mustahabb] for most of it to be given in charity. They said: at the very least, a third should be eaten, a third should be given as gifts and a third should be given in charity. There is another opinion that suggests half may be eaten and half given in charity. This difference of opinion has to do with the amount that is mustahabb. With regard to the other parts of the animal, it is OK to give them in charity . As for eating from it, it is mustahabb but is not waajib (obligatory)… The majority of scholars interpreted this command (i.e., the aayah (interpretation of the meaning): ‘… eat thereof…’ [al-Hajj 22:28 and 36]) as implying encouragement or permission, especially since it came after it had been prohibited.”
Maalik said: “There is no limit to what may be eaten or given in charity or used to feed the poor or the rich, whether one wants to give it uncooked or cooked.” (al-Kaafi, 1/424). The Shaafa’is said that it is mustahabb to give most of it in charity, and said: “At least one third of it may be eaten, and one third given in charity, and one third given away as gifts.” They said that one half may be eaten, but it is more correct to give some of it away in charity.”(Nayl al-Awtaar, 5/145; al-Siraaj al-Wahhaaj, 563). Ahmad said: “We go along with the hadeeth of ‘Abd-Allaah (ibn ‘Abbaas – may Allaah be pleased with them both): ‘He should eat one third himself, feed one third to whomever he wants, and give one third in charity.” (Reported by Abu Moosa al-Isfahaani in al-Wazaa’if; he said it is a hasan hadeeth. This is also the opinion of Ibn Mas’ood and Ibn ‘Umar. No conflicting opinion is known among the Sahaabah. Al-Mughni, 8/632).
The reason why there is a difference of opinion as to how much of the sacrifice may be given in charity is that there are conflicting reports, and some reports were narrated without specifying a particular amount, such as the report of Buraydah (may Allaah be pleased with him) who said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘I had forbidden you to eat from the sacrificial meat for more than three days so that those who could afford it could give to those who are poor, but now you can eat as you wish, feed others from it, and preserve some.’”(Reported by al-Tirmidhi, 1430; he said it is a saheeh hasan hadeeth). The scholars among the Companions of the Prophet and others followed this. And Allaah knows best.