Sahih Bukhari Volume 3, Book 33, Hadith Number 251.
Narated By Ali bin Al-Husain : Safiya, the wife of the Prophet told me that she went to Allah’s Apostle to visit him in the mosque while he was in Itikaf in the last ten days of Ramadan. She had a talk with him for a while, then she got up in order to return home. The Prophet accompanied her. When they reached the gate of the mosque, opposite the door of Um-Salama, two Ansari men were passing by and they greeted Allah’s Apostle. He told them: Do not run away! And said, “She is (my wife) Safiya bint Huyai.” Both of them said, “Subhan Allah, (How dare we think of any evil) O Allah’s Apostle!” And they felt it. The Prophet said (to them), “Satan reaches everywhere in the human body as blood reaches in it, (everywhere in one’s body). I was afraid lest Satan might insert an evil thought in your minds.”