Narrated Ibn 'Umar:
"While the Messenger of Allah (ﷺ) alive, we used to say: 'Abu Bakr, and (then) 'Umar, and (then) 'Uthman.' (JA)
English reference (JA): Vol. 1, Book 46, Hadith 3707 (JA)
Arabic reference (JA): Book 49, Hadith 4072 (JA)