Kautilya's Arthashastra 2.30.50

2.30.50

dvir ahnaḥ snānam aśvānāṃ gandhamālyaṃ ca dāpayet /
kṛṣṇasaṃdhiṣu bhūtejyāḥ śukleṣu svastivācanam //

Horses shall be washed, bedaubed with sandal powder, and garlanded twice a day. On new moon days sacrifice to Bhútas, and on full moon days the chanting of auspicious hymns shall be performed. Not only on the ninth day of the month of Asvayuja, but also both at the commencement and close of journeys (yátra) as well as in the time of disease shall a priest wave lights invoking blessings on the horses.