Shiva Purana
शिष्यस्तद्गुरुणा दत्तं सत्कृत्य शिवपूर्वकम् ॥ भुक्त्वा पश्चाद्द्विराचम्य शिवमन्त्रमुदीरयेत् ॥ ३४ ॥
The disciple shall take the Caru offered by the preceptor, and eat it repeating the name Śiva. After performing the Ācamana twice he shall repeat the mantra of Śiva.
english translation
ziSyastadguruNA dattaM satkRtya zivapUrvakam ॥ bhuktvA pazcAddvirAcamya zivamantramudIrayet ॥ 34 ॥
hk transliteration by Sanscript