It was narrated from Ibn 'Abbas (رضي الله عنه) that

He saw ‘Abdullah bin al-Harith praying, and his hair was braided and tied up at the back. He went and started to undo it, and he did not object to that. Then (when he finished praying) he turned to Ibn 'Abbas and said: What do you have to do with my hair? He said: I heard the Messenger of Allah (ﷺ) say: “The likeness of this one is that of a man who prays with his hands tied behind his back."