Shiva Purana
उदग्गृहीत्वा स्वाहेति देवार्थेऽन्नं यजेत्पुनः ॥ न ममेति वदेदन्ते सर्वत्रायं विधिक्रमः ॥ ६३॥
Taking the north one should chant Svaha and again offer food for the sake of the gods. At the end they say 'It is not mine' This is the order of rituals everywhere.
english translation
udaggRhItvA svAheti devArthe'nnaM yajetpunaH ॥ na mameti vadedante sarvatrAyaM vidhikramaH ॥ 63॥
hk transliteration by Sanscript