Sacrifice is a Sunnah which we love to keep and dislike to abandon

Jundub bin Sufyan al-Bajali (may Allah be pleased with him) said: I was with the Prophet (peace and blessings be upon him) on the day of sacrifice. He (peace and blessings be upon him) said: "Whoever slaughters before offering the prayer, let him sacrifice another animal in its place after praying; and whoever has not yet slaughtered, let him slaughter."

Sayyiduna al-Bara' bin Azib (may Allah be pleased with him) said that his maternal uncle, Sayyiduna Abu Burdah bin Niyar (may Allah be pleased with him), offered his sacrifice before the Prophet (peace and blessings be upon him) had slaughtered. He said: O Messenger of Allah (peace and blessings be upon him), this is a day of meat, so I hastened my sacrifice so that I could feed my family and my neighbours. The Messenger of Allah (peace and blessings be upon him) said: "Repeat the sacrifice." He said: O Messenger of Allah (peace and blessings be upon him), I have a one-year-old young goat which is better than two sheep kept for meat. He (peace and blessings be upon him) said: "It is your best sacrifice, but after you a jadha'ah (a young animal not yet of full age) will not suffice for anyone."

Sayyiduna Anas bin Malik (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) said on the day of sacrifice: "Whoever has sacrificed before the prayer, let him slaughter another animal in its place." A man stood up and said: O Messenger of Allah, this is a day on which meat is craved, and he mentioned something of the need of his neighbours. It was as if the Messenger of Allah (peace and blessings be upon him) confirmed what he said. He said: I have a jadha'ah (a young animal not yet of full age) which is dearer to me than two sheep kept for meat. The narrator said: He (peace and blessings be upon him) granted him a concession, but I do not know whether the concession was for him alone or extended to others besides him.

Ibn Ulayyah (may Allah have mercy on him) mentioned it with his chain, and in it there is the addition: Then the Messenger of Allah (peace and blessings be upon him) turned to two rams and slaughtered them, and the people went to a small flock of sheep and divided it among themselves, or he said: cut it into portions.

Abbad bin Tamim (may Allah have mercy on him) said that Uwaymir bin Ashqar (may Allah be pleased with him) offered his sacrifice before the Eid prayer and informed the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) ordered him to offer another sacrifice in its place.
(b) Bushayr bin Yasar (may Allah have mercy on him) said that Abu Burdah bin Niyar (may Allah be pleased with him) slaughtered before the sacrifice of the Messenger of Allah (peace and blessings be upon him) was slaughtered, and they claim that the Prophet (peace and blessings be upon him) ordered him to repeat the sacrifice. Abu Burdah (may Allah be pleased with him) said: I have only a jadha'ah. The Messenger of Allah (peace and blessings be upon him) said: "If you have only a jadha'ah, then slaughter it."

Imam al-Shafi'i (may Allah have mercy on him) said: It is possible that he ordered the repetition because the sacrifice is obligatory, and it is also possible that (he meant) he should repeat it if he wished to sacrifice, since a sacrifice before its time does not suffice. The sacrifice is not obligatory in such a way that leaving it is impermissible; rather it is a sunnah whose observance we love and whose abandonment we dislike, without holding it to be obligatory. If it is asked: Where is the sunnah that indicates it is not obligatory?
(b) Umm Salamah (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) said: "When the ten days of Dhu al-Hijjah begin, the person who intends to offer a sacrifice should not remove any hair from any part of his body." Imam al-Shafi'i (may Allah have mercy on him) said: This hadith indicates that the sacrifice is not obligatory, because he (peace and blessings be upon him) said: "Whoever intends to offer a sacrifice." Had the sacrifice been obligatory, he (peace and blessings be upon him) would not have said this; rather he would have said: Let no one cut his hair until he has offered the sacrifice.
The Shaykh said: Al-Bara' bin Azib (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) delivered a sermon on the day of sacrifice: "The first thing to do on this day is to offer the prayer, then to sacrifice. Whoever does this has attained our sunnah."

Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) said that a man came to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Allah has made the day of sacrifice a day of Eid for this Ummah." The man said: What if I slaughter the milk-giving animal of my children and family? He (peace and blessings be upon him) said: "Do not slaughter the milk-giving animal; but clip your nails, shave your moustache and remove your pubic hair. In this way you will receive from Allah the reward of a complete sacrifice."

Ibn Wahb (may Allah have mercy on him) mentioned it with his chain in the same way.

Ikrimah narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Three things are obligatory upon me and voluntary for you: offering a sacrifice, praying the witr, and offering the two rak'ahs of the forenoon (duha) prayer."

Ikrimah narrates from Abdullah bin Abbas (may Allah be pleased with them both), attributing it to the Prophet, that he (peace and blessings be upon him) said: "The sacrifice has been made obligatory upon me, but it has not been made obligatory upon you." Al-Asbahani added in his narration: "I have been commanded to offer the forenoon (duha) prayer, but you have not been commanded to do so." [Weak]

Ikrimah narrates from Abdullah bin Abbas (may Allah be pleased with them both), attributing it to the Prophet, that he (peace and blessings be upon him) said: "The sacrifice has been made obligatory upon me, but it has not been made obligatory upon you; and I have been commanded to offer the forenoon (duha) prayer, but you have not been commanded to do so."

Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) led the people in prayer on the day of sacrifice. When he had finished the prayer and the sermon, he called for a ram and slaughtered it himself, and said: "'Bismillahi wallahu akbar' (In the name of Allah, and Allah is the Greatest). O Allah, (this is) on behalf of me and of whoever of my Ummah has not offered a sacrifice."
Imam al-Shafi'i (may Allah have mercy on him) said: It has reached us that Sayyiduna Abu Bakr al-Siddiq and Umar (may Allah be pleased with them both) did not offer sacrifices, fearing that people would follow their example and that whoever saw them would think it obligatory.

Abu Sarihah al-Ghifari (may Allah be pleased with him) said: I found Abu Bakr and Umar (may Allah be pleased with them both) not offering sacrifices. Some narrations make clear that they did so only out of fear of being followed.

Sayyiduna Hudhayfah bin Asid (may Allah be pleased with him) said: I saw Abu Bakr and Umar (may Allah be pleased with them both) not offering sacrifices on behalf of their families, lest people make it a sunnah. But when I came to this land of yours, my family pushed me into jafa' (departing from the sunnah), after I had come to know the sunnah.
This is how Mu'tamir bin Sulayman narrated it from Amir, and he erred in it.

Amr bin Ali said: I said to Yahya bin Sa'id: Mu'tamir narrated to us; he said: Isma'il narrated to us; Mutarrif narrated to us, from al-Sha'bi, from Abu Sarihah. He said: This is like his hadith from al-Sha'bi from Amr al-Jamali, meaning Amr bin Murrah: "Isma'il narrated to us; Amir informed us", and then he mentioned it. Yahya means that he erred in this just as he erred in that. The narration of Sufyan al-Thawri confirms what Yahya said.
Al-Shafi'i said: And (it is also reported) from Sayyiduna Ibn Abbas (may Allah be pleased with them both).

Ikrimah (may Allah have mercy on him), the freed slave of Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both), said that at the time of the sacrifice Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) would give him two dirhams, (saying): Buy meat with them and tell the people that this is the sacrifice of Ibn Abbas (may Allah be pleased with them both).

Sayyiduna Abu Mas'ud al-Ansari (may Allah be pleased with him) said: Despite being well-off, I leave the sacrifice, lest my neighbour think it obligatory upon me.

Sayyiduna Abu Mas'ud Uqbah bin Amr al-Ansari (may Allah be pleased with him) said: Despite my wealth, I resolved to leave the sacrifice, lest the soul consider it binding upon itself.

Abu al-Khasib, a man of Banu Qays bin Tha'labah, came to Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), and a man asked him about something concerning the sacrifice. He said: I dislike, or (he said) avoid (Wahb was in doubt): "the one-eyed animal whose loss of the eye is evident, the lame animal whose lameness is evident, the sick animal whose sickness is evident, and the emaciated animal whose emaciation is evident." Then Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: Perhaps you consider it binding? He said: No, but it is reward, good and sunnah. He said: Yes, that is so.
Imam al-Shafi'i (may Allah have mercy on him) said: The view on sacrifices does not go beyond this, or else they are obligatory, in which case they would be upon everyone, young and old, and nothing less than a sheep would suffice for each person.