All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The meaning of what you are asking about is that he, sallallaahu ‘alayhi wa sallam, used to cover his beard and his cheeks with part of his turban while letting part of its ends hang loose between his shoulder-blades (on his back). This is called 'talahhi' or 'tahneek' by the jurists.
As-Saffaareeni said, “Our scholars said: Tahneek of the turban is when you turn it under the cheek once or twice, and this was (the way of wearing) the turban of the Muslims at the time of the Prophet, sallallaahu ‘alayhi wa sallam.”
Also, the Kuwaiti Fiqh Encyclopedia reads, “Tahneek of the turban (also called talahhi) means turning the turban from under the cheek once or twice. ”
Allaah knows best.