Skandapurana 6.3.159.82

6.3.159.82

oṃ viṣṇurūpa dvijaśreṣṭha bhūdeva paṅktipāvana .
sadakṣiṇā mayā dattā tubhyaṃ vaitaraṇi namaḥ .
iti dānamantraḥ .. 159.82 ..

"Om. O best of the twice-born, whose form is Viṣṇu, O god on earth, sanctifier of assemblies, / [this cow] is given by me along with a priestly gift; homage to you, O Vaitaraṇī!" / Such is the donation mantra.