Shiva Purana
मुखं लिंगमिति प्रोक्तं शिवभक्तशरीरकम् । मृतान्दाहादियुक्तान्वा दाहादिरहितान्मृतान् १४४ ।
It is said that the mouth is the linga (symbol of Shiva) and the body of a Shiva devotee. Whether the deceased is affected by burning or free from burning after death, they are still considered to have passed away.
english translation
mukhaM liMgamiti proktaM zivabhaktazarIrakam । mRtAndAhAdiyuktAnvA dAhAdirahitAnmRtAn 144 ।
hk transliteration by Sanscript