Sahih Bukhari Volume 3, Book 29, Hadith Number 51.

Narated By ‘Abdullah bin ‘Abbas : From As-Sa’b bin Jath-thama Al-Laithi that the latter presented an onager to Allah’s Apostle while he was at Al-Abwa’ or at Waddan, and he refused it. On noticing the signs of some unpleasant feeling of disappointment on his (As-Sab’s) face, the Prophet said to him, “I have only returned it because I am Muhrim.”