صحيح البخاري
From Sahih Bukhari (Hadith 1655):
Narrated `Abdullah bin `Umar:Allah's Messenger (ﷺ) offered a two-rak`at prayer at Mina. Abu Bakr, `Umar and `Uthman, (during the early years of his caliphate) followed the same practice
Reference: Bukhari 1655