Musnad Ahmad 30:2691

Yazid narrated to us, Muhammad informed us, from Abu Salamah, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "You will certainly follow the ways of those who were before you, span by span, and cubit by cubit, and arm's length by arm's length, until even if they were to enter the hole of a lizard, you would enter it with them." They said: "O Messenger of Allah, the Jews and the Christians?" He said: "Who else then?"