Waswas

Waswas (in Arabic وسوس) in Islam is a term for "whispers from Shaytan". When a Muslim has some thoughts against Islam, he disregards them as waswas - a voice of Shaytan.

Waswas in the Qur'an

The Arabic word وسوس (waswas) in various forms appears 5 times in the Qur'an.

The first two refer to the story of Adam and Eve. The fa- prefix means "but" or "then".

But the Shaitan made an evil suggestion (فَوَسْوَسَ, fa-waswasa) to them that he might make manifest to them what had been hidden from them of their evil inclinations, and he said: Your Lord has not forbidden you this tree except that you may not both become two angels or that you may (not) become of the immortals.

Quran 7:20

But the Shaitan made an evil suggestion (فَوَسْوَسَ, fa-waswasa) to him; he said: O Adam! Shall I guide you to the tree of immortality and a kingdom which decays not?

Quran 20:120

Then one time it's a persons soul which whispers. The tu- simply indicates present tense, 3rd person, feminine, singular verb.

And We have already created man and know what his soul whispers (تُوَسْوِسُ, tuwaswisu) to him, and We are closer to him than [his] jugular vein

Quran 50:16

And two times in a short sura 114. The al- indicates definite article (before a noun). The yu- indicates present tense, 3rd person, singular, masculine verb.

114:1 Say: I seek refuge in the Lord of men,

114:2 The King of men,

114:3 The god of men,

114:4 From the evil of the retreating whisperer (ٱلْوَسْوَاسِ, al-waswasi)

114:5 Who whispers (يُوَسْوِسُ, yuwaswisu) into the hearts of men,

114:6 From among the jinn and the men.

Quran 114:1-6

Tafsir Al-Jalalayn says that the "whisperer" in 114:4 is Satan:

from the evil of the slinking whisperer Satan — he is referred to by the name of the action waswasa on account of his repeated engaging in it — who slinks away and recoils from the heart whenever God is mentioned

Tafsir Al-Jalalayn on 114:4

From this we can conclude that the concept of waswas (Satan whispering into Muslim minds) is described in the Qur'an, so it is definitely a part of the Islamic doctrine.

Waswas in hadith

Muslims are forgiven thoughts against Islam (the "whispers from Satan") as long don't act upon them and keep silent:

Narrated Abu Huraira: The Prophet (ﷺ) said, "Allah has accepted my invocation to forgive what whispers (وَسْوَسَتْ, waswasat) in the hearts of my followers, unless they put it to action or utter it."

Sahih Bukhari 3:46:705

Narrated Abu Huraira: The Prophet (ﷺ) said, "Allah forgives my followers those (evil deeds) their souls may whisper (وَسْوَسَتْ, waswasat) or suggest to them as long as they do not act (on it) or speak."

Sahih Bukhari 8:78:657

It was narrated that Abu Hurairah said: "The Messenger of Allah said: 'Allah, the Mighty and Sublime, has forgiven my Ummah for what is whispered (وَسْوَسَتْ) to them or what enters their minds, so long as they do not act upon it or speak of it.'"

Sunan an-Nasa'i 27:3464:1 (Sahih)

Most of the whispers come from urinating in a place for bathing:

It was narrated from 'Abdullah bin Mughaffal that the Prophet (ﷺ) said:

"None of you should urinate in the place where he bathes, for most Waswas (devilish whispers) [1] come from that." [1] I.e., with regard to whether the urine has soiled his body or not.

Sunan an-Nasa'i 1:36:1