In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Al-Allaamah Saaleh Al-Fawzaan [may Allaah preserve him] said:
The meaning of ‘Naseehah’ is Al-Khuloos [purity]. It is said that something is ‘Naasih’ meaning: It is free from deceit. And it is said: ‘Asalun Naasihun’ [Pure Honey]; Labanun Naasihun [Pure Milk]- meaning: Free from deceit and bad mixtures. This is how it is [with regards] to the religion of Islaam, for indeed it is free from every falsehood and deception, cheating and treachery. It is a pure and unadulterated religion. Likewise, the Muslim’s apparent [affairs] are the same as his hidden [affairs]- upon purity and safe from evil manners, treachery, betrayal and other than that. As for the one who cheats, deceives and plots, or his apparent [affairs] are in opposition to his hidden [affairs], this trait is not from the Religion. [Source: An Excerpt from ‘Minhatur-Rabbaaniyyah Fee Sharhi Ar-ba’een An-Nawawiyyah’- page 12]