Vaishnava Dharmashastra 22.22

22.22

brāhmaṇasya kṣatriviṭśūdreṣu sapiṇḍeṣu ṣaḍrātratrirātraikarātraiḥ ||

A Brâhmana (to whom) Sapindas of the Kshatriya, Vaisya, or Sûdra castes (have been born or have died) becomes pure within six nights, or three nights, or one night, respectively.