كتاب الهبة وفضلها والتحريض عليها
Read the English translation first, with the original Arabic directly underneath.
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 Messenger (ﷺ) 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)
أَمَا إِنَّا لَمْ نَرُدَّهُ عَلَيْكَ إِلاَّ أَنَّا حُرُمٌ