It is narrated from the sixth Shia Imam, Jafar Al-Sadeq (AS) who said:

Indeed, if the scholar does not practice what he preaches, his words and preaching will slide from the hearts and pass from them (do not stay in the hearts), as the rain water slides on the shiny, smooth and impenetrable surface of the stone and passes it [1].

[1] Al-Kafi, Vol. 1, Page 44.

Source: en.shafaqna.com