SB 8.16.26

sinīvālyāṁ mṛdālipya
 snāyāt kroḍa-vidīrṇayā
yadi labhyeta vai srotasy
 etaṁ mantram udīrayet
Word for word: 
sinīvālyām — on the dark-moon day; mṛdā — with dirt; ālipya — smearing the body; snāyāt — one should bathe; kroḍa-vidīrṇayā — dug up by the tusk of a boar; yadi — if; labhyeta — it is available; vai — indeed; srotasi — in a flowing river; etam mantram — this mantra; udīrayet — one should chant.
Translation: 
If dirt dug up by a boar is available, on the day of the dark moon one should smear this dirt on his body and then bathe in a flowing river. While bathing, one should chant the following mantra.