Srimad-Bhagavatam: Canto 8 - Chapter 1 - Verse 41
Sanskrit:
निवेदितं तद्भक्ताय दद्याद्भुञ्जीत वा स्वयम् ।दत्त्वाचमनमर्चित्वा ताम्बूलं च निवेदयेत् ॥ ४१ ॥
ITRANS:
niveditaṁ tad-bhaktāyadadyād bhuñjīta vā svayamdattvācamanam arcitvātāmbūlaṁ ca nivedayet
Translation:
One should offer all the prasāda to a Vaiṣṇava or offer him some of the prasāda and then take some oneself. After this, one should offer the Deity ācamana and then betel nut and then again worship the Lord.