From Sahih Bukhari (Hadith 2596):
Narrated `Abdullah bin `Abbas:That he heard As-Sa'b bin Jath-thama Al-Laithi, who was one of the companions of the Prophet, saying that he gave the meat of an onager to Allah's Messenger (ﷺ) while he was at a place called Al-Abwa' or Waddan, and was in a state of Ihram. The Prophet (ﷺ) did not accept it. When the Prophet (ﷺ) saw the signs of sorrow on As-Sa'b's face because of not accepting his present, he said (to him), "We are not returning your present, but we are in the state of Ihram." (See Hadith No)
Reference: Bukhari 2596