It is narrated from Sayyiduna Ubaydullah bin Umar (may Allah have mercy on him) that when Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) prostrated with a turban on his head, he would push the turban back and place his forehead on the ground.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2661