Sahih Bukhari Volume 4, Book 55, Hadith Number 658.

Narated By Abu Huraira : Allah’s Apostle said “How will you be when the son of Mary (i.e. Jesus) descends amongst you and he will judge people by the Law of the Quran and not by the law of Gospel (Fateh-ul Bari page 304 and 305 Vol 7)