He passed by Al-Hasan bin Ali while he was performing Salat and he had gathered his locks at the back of his head, so he (Abu Rafi) undid them, and Al-Hasan turned to him angrily. He said: "Resume your Salat and do not be angry, for indeed I heard Allah's Messenger (S) saying: 'That is the seat of Ash-Shaitan.'"
Reference: Jami` at-Tirmidhi 384 In-book : Book 2, Hadith 236 English translation : Vol. 1, Book 2, Hadith 384
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