Al-Sha'bi (may Allah have mercy on him) narrates from Safwan bin Muhammad or Muhammad bin Safwan (may Allah be pleased with him) that he hunted two rabbits and found no iron implement with which to slaughter them, so he slaughtered them with a stone. Then he told the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) "permitted him to eat the rabbits."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19394