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 Messenger of Allah (S) saying: 'That is the seat of Ash-Shaitan.'"  

أَقْبِلْ عَلَى صَلاَتِكَ وَلاَ تَغْضَبْ فَإِنِّي سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ ذَلِكَ كِفْلُ الشَّيْطَانِ قَالَ وَفِي الْبَابِ عَنْ أُمِّ سَلَمَةَ وَعَبْدِ اللَّهِ بْنِ عَبَّاسٍ