It was narrated from Kathir bin 'Abdullah bin 'Amr bin 'Awf Al-Muzani, from his father, that his grandfather said:
"The Messenger of Allah (ﷺ) said: 'Start with the horses on the day that you bring (the animals to drink).' "
English reference: Vol. 3, Book 16, Hadith 2484
Arabic reference: Book 16, Hadith 2578