Skandapurana 5.57.23

5.57.23

asmātsthānātsamīpasthaṃ vāruṇyāṃ diśi puṇyakṛt ..
kṛṣṇāṃgārakaṣaṣṭhyāṃ yo naraḥ snānaṃ samācaret .. 23 ..

near to this place, in the western direction, producing merit. / The man who performs a ritual ablution on the sixth day of the dark fortnight falling on a Tuesday (kṛṣṇāṅgārakaṣaṣṭhī),