When they do this, they'll go astray...

Abu Hurairah records that the Prophet, sallAllaahu 'alayhi wa sallam, said:

"For a time this community will practice the teachings of the Book of Allaah. Then for some time they will adhere to the path of the Prophet (sallAllaahu 'alayhi wa sallam). Then they will start acting on the strength of their own opinions. And when they do this, they will go astray."

[Jami' Bayan al-'Ilm]