Srimad Bhagavatam Canto 04, Chapter 06, Text 36

SB 4.6.36

lingam ca tapasabhistam
bhasma-danda-jatajinam
angena sandhyabhra-ruca
candra-lekham ca bibhratam
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
He was seated on a deerskin and was practicing all forms of austerity. Because his body was smeared with ashes, he looked like an evening cloud. On his hair was the sign of a half-moon, a symbolic representation.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
 
Lord Siva’s symptoms of austerity are not exactly those of a Vaisnava. Lord Siva is certainly the number one Vaisnava, but he exhibits a feature for a particular class of men who cannot follow the Vaisnava principles. The Saivites, the devotees of Lord Siva, generally dress like Lord Siva, and sometimes they indulge in smoking and taking intoxicants. Such practices are never accepted by the followers of Vaisnava rituals.
Srimad Bhagavatam Canto 04, Chapter 06, Text 35
Srimad Bhagavatam Canto 04, Chapter 06, Text 37