Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: Whoever matted his hair, or braided it, or tied it in a knot should have his head shaved.
This is the authentic (version): from Abdullah (bin Dinar), from Ibn Umar as his own saying, and from Nafi', from Ibn Umar, from Umar (may Allah be pleased with him) as his own saying.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9587