Musannaf Ibn Abi Shayba 38:121

Waki’ narrated to us, from Sufyan, from Habib, from Abu al-Bakhtari, who said: When the day of Siffin arrived and the war intensified, ‘Ammar called for a drink of milk. He drank it and said: "Indeed, the Messenger of Allah (may Allah bless him and grant him peace) said to me: 'The last drink you will drink from the world is a drink of milk.'"