Skandapurana 16.46.5

16.46.5

tatastuṣṭamanā devo grahatvaṃ tasya taddadau ..
taṃ saṃpūjya vidhānena somaputrapratiṣṭhitam..
saumyāṣṭamyāṃ viśeṣeṇa rājasūyaphalaṃ labhet .. 5 ..

Then, with a pleased mind, the god granted him status as a planet. / Having worshipped according to rule that [liṅga] installed by the son of Soma, / particularly on a Wednesday eighth [lunar day], one obtains the fruit of a Rājasūya sacrifice.