Safiyyah bint Huyai (May Allah be pleased with him), the Mother of the Believers, said: I came to visit the Prophet (PBUH) while he was in the state of I`tikaf [(seclusion) in the mosque during the last ten days of Ramadan]. After having talked to him, I got up to return. The Prophet (PBUH) also got up with me and accompanied me a part of the way. At that moment two Ansari man passed by. When they saw him they quickened their pace. The Prophet (PBUH) said to them, "Do not hurry. She is Safiyyah, daughter of Huyai, my wife.'' They said: "Subhan Allah (Allah is free from imperfection)! O Messenger of Allah! (You are far away from any suspicion).'' The Messenger of Allah (PBUH) said, "Satan circulates in a person like blood (in the blood streams). I apprehended lest Satan should drop some evil thoughts in your minds.''
[Al-Bukhari and Muslim].

Commentary: Even just a passing thought of some thing undesirable about the Prophet (PBUH) is dangerous for belief. In order to put an end to this evil suspicion, he stopped the two Companions and explained to them the situation. This was done lest the devil may create some doubt in the mind of the two Companions. The conclusion is that, if at any place there is some far fetched chance of creation of bad opinion about somebody, then it is necessary to give an explanation lest some doubt may arise in some body's mind. This is particularly essential for `Ulama', who should remain aloof from such occasions and places, lest the people may start doubting their integrity and piety.