(a) Sa'id bin Abi Sa'id al-Maqburi narrates from his father that he saw Abu Rafi' (may Allah be pleased with him), the freed slave of the Prophet (peace and blessings be upon him), pass by Hasan bin Ali (may Allah be pleased with them both). He (may Allah be pleased with him) was praying, and he had made his locks into braids and tucked them behind his neck. Abu Rafi' (may Allah be pleased with him) undid those braids. Sayyiduna Hasan (may Allah be pleased with him) turned towards him in anger, so Abu Rafi' (may Allah be pleased with him) said: Carry on with your prayer and do not be angry, for I heard the Messenger of Allah (peace and blessings be upon him) say: "These braids of hair are the sitting place of Satan," meaning that tying the braids into a knot is forbidden.
(b) In the narration of Abd al-Razzaq, he (peace and blessings be upon him) said: "This is the sitting place of Satan."
(c) Narrations about the dislike of such a knot from Sayyiduna Umar, Ali, Hudhayfah and Abdullah bin Mas'ud (may Allah be pleased with them) have already passed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2680