Sahih Muslim Book 032, Hadith Number 6276.
Chapter : It is forbidden to curse the beasts.
'Imran b. Husain reported: We were with Allah's Messenger (may peace be upon him) in some of his journeys and there was a woman from the Ansar riding a she-camel that it shied and she invoked curse upon that. Allah's Messenger (may peace be upon him) heard it and said: Unload that and set it free for it is accursed. 'Imran said: I still perceive that (dromedary) walking amongst people and none taking any notice of that.