Srimad Bhagavatam Canto 04, Chapter 07, Text 17

SB 4.7.17

vaisnavam yajña-santatyai
tri-kapalam dvijottamah
purodasam niravapan
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Thereafter, in order to resume the activities of sacrifice, the brahmanas first arranged to purify the sacrificial arena of the contamination caused by the touch of Virabhadra and the other ghostly followers of Lord Siva. Then they arranged to offer into the fire the oblations known as purodasa.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Lord Siva’s followers and devotees, headed by Virabhadra, are known as viras, and they are ghostly demons. Not only did they pollute the entire sacrificial arena by their very presence, but they disturbed the whole situation by passing stool and urine. Therefore, the infection they had created was to be first purified by the method of offering purodasa oblations. A visnu-yajña, or an offering to Lord Visnu, cannot be performed uncleanly. To offer anything in an unclean state is called a sevaparadha. The worship of the Visnu Deity in the temple is also visnu-yajña. In all Visnu temples, therefore, the priest who takes care of the arcana-vidhi must be very clean. Everything should be always kept neat and clean, and the foodstuffs should be prepared in a neat and clean manner. All these regulative principles are described in The Nectar of Devotion. There are thirty-two kinds of offenses in discharging arcana service. It is required, therefore, that one be extremely careful not to be unclean. Generally, whenever any ritualistic ceremony is begun, the holy name of Lord Visnu is first chanted in order to purify the situation. Whether one is in a pure or impure condition, internally or externally, if one chants or even remembers the holy name of the Supreme Personality of Godhead Visnu, one immediately becomes purified. The yajña arena was desecrated by the presence of Lord Siva’s followers, headed by Virabhadra, and therefore the entire arena had to be sanctified. Although Lord Siva was present and he is all-auspicious, it was still necessary to sanctify the place because his followers had broken into the arena and committed so many obnoxious acts. That sanctification was possible only by chanting the holy name of Visnu, Trikapala, which can sanctify the three worlds. In other words, it is admitted herein that the followers of Lord Siva are generally unclean. They are not even very hygienic; they do not take baths regularly, they wear long hair, and they smoke gañja. Persons of such irregular habits are counted amongst the ghosts. Since they were present in the sacrificial arena, the atmosphere became polluted, and it had to be sanctified by trikapala oblations, which indicated the invocation of Visnu’s favor.
Srimad Bhagavatam Canto 04, Chapter 07, Text 16
Srimad Bhagavatam Canto 04, Chapter 07, Text 18