Sahih Bukhari | Volume 9 | Hadith Number 421

Narrated by Abu Huraira
The Prophet said, "The Hour will not be established till my followers copy the deeds of the previous nations and follow them very closely, span by span, and cubit by cubit (i.e., inch by inch)." It was said, "O Allah's Apostle! Do you mean by those (nations) the Persians and the Byzantines?" The Prophet said, "Who can it be other than they?"