Shiva Purana
शांभवी चैव शाक्ती च मांत्री चैव शिवागमे ॥ दीक्षोपदिश्यते त्रेधा शिवेन परमात्मना ॥ ६ ॥
The initiation as ordained by Śiva the great Ātman in the Śivāgama is threefold—pertaining to Śiva, Śakti and mantra.
english translation
zAMbhavI caiva zAktI ca mAMtrI caiva zivAgame ॥ dIkSopadizyate tredhA zivena paramAtmanA ॥ 6 ॥
hk transliteration by Sanscript