Abu Amr said:

It has reached me that whenever a man preaches to others while not seeking the Face of Allah, that the hearts will slip away from him as the water slips of from the surface of [Mount] Safaa.


[1] Tahzeeb Hilyat Al-Awliyaa 2/290

عن الأوزاعي أنه قال: بلغني أنه ما وعظ  رجل قوما لا يريد به وجه الله إلا زلت عنه القلوب كما زل الماء عن الصفا