Shiva Purana
तत्र पूर्वं त्रयोदश्यां सुस्नातः सुकृताह्निकः ॥ अनुज्ञाप्य स्वमाचार्यं संपूज्य प्रणिपत्य च ॥ ४ ॥
Earlier on the thirteenth day of the month he had taken a good bath and performed ritualistic ceremonies. Having obtained permission he worshiped his teacher and bowed down to him.
english translation
tatra pUrvaM trayodazyAM susnAtaH sukRtAhnikaH ॥ anujJApya svamAcAryaM saMpUjya praNipatya ca ॥ 4 ॥
hk transliteration by Sanscript