Sa'id bin Jubayr (may Allah have mercy on him) narrates from Ibn Abbas (may Allah be pleased with them both) that one side of a wild donkey was given to the Prophet (peace and blessings be upon him) as a gift, and he (peace and blessings be upon him) returned it, because he (peace and blessings be upon him) was in the state of ihram.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9932