Garudapurana 1.23.7

1.23.7

sūryopasthānakaṃ kṛtvā sūryamantraiḥ prapūjayet /
oṃ hāṃ hīṃ hūṃ haiṃ hauṃ haḥ śivasūryāya namaḥ /
oṃ haṃ khakholkāya sūryamūrtaye namaḥ /
oṃ hrāṃ hrīṃ saḥ sūryāya namaḥ //

Having performed the adoration of the Sun, one should worship with the Sun mantras: / "Oṃ hāṃ hīṃ hūṃ haiṃ hauṃ haḥ, salutation to Śiva-Sūrya; / Oṃ haṃ, salutation to Khakholka, the form of the Sun; / Oṃ hrāṃ hrīṃ saḥ, salutation to Sūrya."