Ibn Abbas (may Allah be pleased with them both) says that Sa'b bin Jaththamah (may Allah be pleased with him) gave the Prophet (peace and blessings be upon him) a wild donkey as a gift while he (peace and blessings be upon him) was in the state of ihram. He (peace and blessings be upon him) returned it to him and said: "Had we not been in the state of ihram, we would have accepted it from you."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9931