Uthman bin Ata narrates from his father that a man came to Ibn Umar (may Allah be pleased with them both) while he was in the mosque of Mina, and asked him about letting the end of the turban hang down. Ibn Umar (may Allah be pleased with them both) said to him: I will tell you about it, if Allah wills, with knowledge. The Messenger of Allah (peace and blessings be upon him) sent out a military detachment, appointed Abdur-Rahman bin Awf (may Allah be pleased with him) as its commander, tied a banner for him and said: "Take it, Bismillah wa barakatillah (in the name of Allah and with the blessing of Allah)." And he said: Abdur-Rahman (may Allah be pleased with him) was wearing a turban of coarse cotton dyed black. The Messenger of Allah (peace and blessings be upon him) called him, undid his turban, then tied it for him with his own hand, leaving the end of his turban hanging about four fingers' length or so, and he said: "Wear the turban like this, for it is better and more beautiful."
Uthman bin Ata is not strong (in narration).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 13065