Abu Rafi passed by Hasan bin Ali, peace be upon them, while he was praying standing, and he had tucked his braid into the back of his neck. So Abu Rafi undid it. Hasan turned to him angrily, and Abu Rafi said, "Attend to your prayer and do not be angry, for I heard the Messenger of Allah ﷺ say that this is the seat of Satan," meaning the place where the braid is tucked.
حدثنا الحسن بن علي حدثنا عبد الرزاق عن ابن جريج حدثني عمران بن موسى عن سعيد بن أبي سعيد المقبري يحدث عن أبيه أنه رأى
مر بحسن بن علي عليهما السلام وهو يصلي قائما وقد غرز ضفره في قفاه فحلها أبو رافع فالتفت حسن إليه مغضبا فقال أبو رافع أقبل على صلاتك ولا تغضب فإني سمعت رسول الله ﷺ يقول ذلك كفل الشيطان يعني مقعد الشيطان يعني مغرز ضفره
[Its isnad is hasan] Tirmidhi narrated it in the Book of Prayer, chapter on the dislike of gathering up the hair during prayer, hadith no. 384, from the hadith of Abdul-Razzaq with this chain, and he said, "Hasan." It is also found in Musannaf Abdul-Razzaq, hadith no. 2991. Ibn Khuzayma graded it sahih, hadith no. 911, as did Ibn Hibban, hadith no. 474, and Hakim, 1/261, 262, and Dhahabi concurred with him. 1/261.