كتاب الحج
15  
The Book of Pilgrimage
(65)
Chapter: It is permissible to ride the sacrificial animal if necessary
(65)
باب جَوَازِ رُكُوبِ الْبَدَنَةِ الْمُهْدَاةِ لِمَنِ احْتَاجَ إِلَيْهَا ‏‏
Sahih Muslim 1324 b

Abu Zubair reported:

I asked Jabir (Allah be pleased with him) about riding on the sacrificial animal, to which he replied: I heard Allah's Apostle (ﷺ) as saying: Ride on them gently until you find another mount.
وَحَدَّثَنِي سَلَمَةُ بْنُ شَبِيبٍ، حَدَّثَنَا الْحَسَنُ بْنُ أَعْيَنَ، حَدَّثَنَا مَعْقِلٌ، عَنْ أَبِي الزُّبَيْرِ، قَالَ سَأَلْتُ جَابِرًا عَنْ رُكُوبِ الْهَدْىِ، فَقَالَ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ ‏ "‏ ارْكَبْهَا بِالْمَعْرُوفِ حَتَّى تَجِدَ ظَهْرًا ‏"‏ ‏.‏
Reference : Sahih Muslim 1324b
In-book reference : Book 15, Hadith 419
USC-MSA web (English) reference : Book 7, Hadith 3053
  (deprecated numbering scheme)