In Hadith, Hazrat Anas (r.a.) narrated that Rasulullah (s.a.s.) said Shaytaan travels through the body like blood.
Explanation by Imam Al-Bukhari and Imam Muslim: Allah gave full power to Shaytaan to put evil ideas into the hearts of men. If a man does not act upon these ideas, he has passed the worldly examination and will get a high place in Jinnah (Heaven). When we say that the Shaytaan travels through the body like blood, it means not physically but according to his evil ideas or thinking there are things that travel like the human blood.
In Hadith Hazrat Imam Abu Hanifah (r.a.) related that the Nabi (s.a.s.) said:
“The was-wâs that enters the hearts of my ummah Allah has forgiven, as long as they don’t act upon or voice it.” [Imam Al-Bukhari and Imam Muslim agree on it]
Tafsir (Commentary): Was-wâs is the bad intentions that enters one’s heart. And those good intentions that enter one’s heart is called ilham. The ilham won’t be accepted unless it is accordance with the Holy Qur’an and Hadith. Bad thoughts by a person that is not related to aqeeda (belief), and doesn’t act on them, for him is Maafoo (forgiveness). If vice versa is related to kufr (disbelief), then it will be kufr. And if related to dhal (straying away), then it will be dhalleen. For both of these situations, tawba is fardh (obligatory). If this intention is related to any actions and not aqa’id (belief), and he keeps this intention in his heart, then he is a sinner.
Question: Does the commission of sin remove one from Islam?
Hazrat Anas bin Malik relates Rasulullah said that three things form the foundation of Al-Islam.