Sayyiduna Anas bin Malik (may Allah be pleased with him) said: I saw the Prophet (peace and blessings be upon him) performing ablution, and he (peace and blessings be upon him) was wearing a Qatari turban. He (peace and blessings be upon him) put his hand under the turban and wiped the front part of his head, but did not undo the turban.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 281