Hazrat Moulana Ashraf Ali Thanwi (rahmatullahi ‘alaih) once mentioned the following:
A person cannot trust his nafs at any time nor feel safe from its harm. Even though one may reach great heights in piety and perform miracles, or one may become a learned ‘aalim or great wali, but at no point can he feel safe and secure of the evils of his nafs (as he does not know at which point the nafs will lure him towards evil and sin).
(Malfoozaat Hakeemul Ummat 13/116)
Source: Ihyaauddeen.co.za