Manava Dharmashastra 5.108

5.108

mṛttoyaiḥ śudhyate śodhyaṃ nadī vegena śudhyati
rajasā strī manoduṣṭā saṃnyāsena dvijottamāḥ //

By earth and water is purified what ought to be made pure, a river by its current, a woman whose thoughts have been impure by the menstrual secretion, a Brahmana by abandoning the world (samnyasa).