Sahih Bukhari Volume 8, Book 76, Hadith Number 586.

Narated By Ibn Al-Musaiyab : The companions of the Prophet said, “Some men from my companions will come to my Lake-Fount and they will be driven away from it, and I will say, ‘O Lord, my companions!’ It will be said, ‘You have no knowledge of what they innovated after you left: they turned apostate as renegades (reverted from Islam).