Lord kAlAgni rudra teaches bhusu.ndi - earth came out of the sadyojAta face of the Lord. From this came the gray colored cow called nanda from the dung of which came vibhUti. From the vAmadeva face came the water, from that came the black colored cow bhadra giving bhasita. From the aghora face came the fire, from that the copper colored cow t the copper colored cow surabhi giving bhasma. From the tatpuruSha face came the gas/air, from which came shAnti and from that came the white colored cow sushIle giving xAra. From the IshAna face came the space, from which came the multi colored cow sumanA giving raksha.
The Holy Ash which is called by five names, when pronunced raises the spiritual power of the individual and hence is called vibhUti. Since it burns the sins to ashes it is called bhasita. Since it gives the wisdom to all it is called bhasmam. Since it neutralises the bad things it is called xAra. Since it protects the people from evil forces, it is called raxa.
Irrespective of caste, creed, sex and all other differences all the people shall wear the Holy Ash. It is an old adage the says the forehead without the ash is a ruined one. The Holy Ash having the powers of agni and soma refreshes the one who wears it. For the seekers of yoga this Holy Ash kindles the spirit and provides early fruit. When wearing the Holy Ash the mantra shivAya namaH(The Holy Five Letters(1)) is chanted or the sadyojAtAdi paJNcha brahma mantra(2) or the tryambakaM ormAno mahAntam from rudra sUktam(3).
The Holy Ash purifies the one who wears it. This purification (bath) is called Agneya snAna. In this the renouced ones would smear the ash in the remains of ritual fire from the leg to the head. Others would smear in the ash from the head to the leg.
ska.ndha purANam says that the Holy Ash would have to be worn at the following fifteen places in the body.