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.