It is narrated from Imam Sadeq (AS) who said:

Indeed, if a scholar does not practice according to his/her knowledge, his/her words and preaching will not shake hearts and has no effect, as the rain water pours on smooth surface of hard impenetrable stone and does not pass through it [1].

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

Source: en.shafaqna.com