(6) باب قَبُولِ الْهَدِيَّةِ
Narrated As-Sa'b bin Jath-thama:
An onager was presented to Allah's Messenger (ﷺ) at the place called Al-Abwa' or Waddan, but Allah's Apostle rejected it. When the Prophet (ﷺ) noticed the signs of sorrow on the giver's face he said, "We have not rejected your gift, but we are in the state of Ihram." (i.e. if we were not in a state of Ihram we would have accepted your gift, Fath-ul-Bari page 130, Vol. 6)
Reference: Sahih al-Bukhari 2573
In-book reference: Book 51, Hadith 8
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 47, Hadith 747