Vaishnava Dharmashastra 65.2

65.2

aśvinoḥ prāṇas tau ta iti jīvādānaṃ dattvā yuñjate mana ity anuvākenāvāhanaṃ kṛtvā jānubhyāṃ pāṇibhyāṃ śirasā ca namaskāraṃ kuryāt ||

Having called up in his mind (Vishnu to life, with the Mantra), 'The two Asvins possess life, may they (give you life),'and having invited (Vishnu) with the Anuvâka (beginning with the words), 'They get their minds ready,' he must worship him with his knees, his hands, and his head.
[LXV, LXVI. These two chapters treat of the worship of Vishnu. (Nand.)
LXV. 1. The fittest. place for worshipping Vishnu is upon a Sâlagrâma (ammonite) stone. (Nand.)
2. 1 Kâthaka XI, 7. The rendering of this Mantra is conjectural, as the reading is uncertain. Nand. states expressly that it is quoted from the Kâthaka.--2 See LXIV, 22.--3 'The particle ka indicates that he must also worship Vishnu in his mind, and with his speech, by saying, 'Om, adoration to Bhagavat Vâsudeva.' (Nand.)]