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