(a) Al-Hasan al-Basri (may Allah have mercy on him) says that when the Companions of the Messenger of Allah (peace and blessings be upon him) (may Allah be pleased with them) prostrated, their hands would be inside their clothes, and some of them would prostrate on their turbans.
(b) In the first of these hadiths, the garment means a cloth meant only to be placed for prostration (such as a handkerchief, a sheet and the like), and in the second narration it is possible that some people used to prostrate on their turban and their forehead; but caution in prostration is better.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2667