Nafi' narrates from Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever sends off a voluntary sacrificial animal and it perishes, no replacement is due from him. If it was from a vow, a replacement is due from him." It has been narrated thus with this chain from al-Awza'i, and I consider it a mistake.
Others narrated it from al-Awza'i from Abdullah bin Amir al-Aslami, and it is characteristic of Abdullah bin Amir to raise mawquf reports (to the Prophet). And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10257