Natyashastra
आवाहे च विवाहे च यज्ञे नृपतिमङ्गले । नान्दीशब्दमुपश्रुत्य हिंस्रा नश्यन्ति चैव हि ॥ २५॥
In ceremonies such as invitations, weddings, and sacrifices, upon hearing the auspicious Nandi sound, harmful or destructive forces are dispelled.
english translation
AvAhe ca vivAhe ca yajJe nRpatimaGgale । nAndIzabdamupazrutya hiMsrA nazyanti caiva hi ॥ 25॥
hk transliteration by Sanscript