Skandapurana 10.80

10.80

oṃ yamadvāre mahāghore yā sā vaitaraṇī nadī .
tartukāmo dadāmyenāṃ tubhyaṃ vaitaraṇi namaḥ .
ityadhivāsanamantraḥ .. 159.80 ..

“Oṃ. The river that is the Vaitaraṇī at the terrible door of Yama—
desiring to cross it, I give this [cow]; homage to you, O Vaitaraṇī!”
Such is the mantra of preliminary consecration.