It is narrated on the authority of 'Abdullah bin Mas'ud that the Apostle (ﷺ) was asked about evil prompting, to which he replied: It is pure faith.
Explanation & Benefits
Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary: Benefits and Issues:
The cause or reason for waswasah (whisperings) is faith (iman),
because Shaytan casts waswasah into the heart of the one whom he has despaired of leading astray.
And as for those who are disbelievers (kuffar) and sinners (fussaq) and are already under his control, there is no need for him to cast waswasah into their hearts.
Therefore, waswasah is a sign of faith,
provided that a person finds it detestable.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 342