Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates that he saw Sayyiduna Abdullah bin al-Harith (may Allah be pleased with him) praying while his hair was tied up behind him, so he began to undo it. When he finished the prayer, he said: "I heard the Messenger of Allah (peace and blessings be upon him) say: 'The likeness of one who prays with his hair tied up is that of one who prays with his hands tied.'"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12144