This is also worth noting that in the verse:
From the mischief of the Whisperer (of Evil), who withdraws (after his whisper). Surah Naas (114:4)
It is not said that seek refuge from the mischief of whispering of the whisperer, but to seek refuge from the mischief of the whisperer. This shows that the whisperer has other malice apart from evil whispering. Thus, we should seek refuge from all malice of the whisperer. For e.g., the whisperer might goad someone else to do something which angers one, and in that anger that person does something which leads to humiliation and harm in this world and the hereafter.
Thus, it is frequently seen that in a gathering of friends, everyone is talking with each other and someone very candidly says something which someone else finds offensive. Others take pleasure from this. This talk leads to not only quarrels, abuses but sometimes even fights. This is in fact the malice of the whisperer at work. In the guise of friendship, he (or she) made the other person say that thing and that person got carried away in anger.
Maybe this is the reason that the Holy Prophet (Sallallahu alaihi wa sallam) said, quoted by Mundhiri (May Allah shower His Mercy on him) in At Targheeb Wat Tarheeb, a person cannot reach true faith unless and until he (or she) leaves jesting and lying.
“Wasaawis” with the Fath is a noun and with the Kasra is a root word. It is the rustle of the wind. The sound made by jewelry moving is also termed as that. Although the whisper is in the heart where sound does not exist, but as it has words (orders/persuasions) in it and they are related to sounds, the word “waswasa” is used for it. It means a slight sound.
As whispers strike repeatedly, the word “waswasa” has also been used multiple times so that the repetition of the word indicates the repetitive nature of the whispers.
More often than not, this word is used for negative things, which strike the heart. Thus, they are also called “satanic whispers.”
[Excerpted from Maqasid Ul Islam, Vol. 8, Pg. No. 96, 97]