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).' " (ID)
English reference (ID): Vol. 3, Book 16, Hadith 2484 (ID)
Arabic reference (ID): Book 16, Hadith 2578 (ID)