Abu Salamah and Sulayman bin Yasar (may Allah have mercy on them both) say that the Messenger of Allah (peace and blessings be upon him) said: "Whoever wishes to delay the sacrifice may perform it until the end of Dhul-Hijjah."
(b) In the narration of Abu Hamid, the Prophet (peace and blessings be upon him) said: "The sacrifices may be delayed until the new moon of Muharram is sighted."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19256
Abu Umamah bin Sahl bin Hunayf (may Allah be pleased with him) says: When one of the Muslims bought a sacrificial animal, he would fatten it and then slaughter it after al-Adha, at the end of Dhul-Hijjah.
Note: In some narrations it has come that the sacrifice may be made until the beginning of Muharram. If these narrations are authentic, this is a latitude; otherwise, in the authentic narrations the days of Mina are counted as the days of sacrifice.
The hadith of Abu Salamah and Sulayman is mursal, and the hadith of Abu Umamah is a report from people who are not named. Al-Shaykh (may Allah have mercy on him) said: Both are open to question: this one because it is mursal, and the earlier one because of the narrators' disagreement over it from Sulayman bin Musa; and the hadith of Sulayman bin Musa is the more fitting of the two to be adopted. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19257