Manava Dharmashastra 11.106

11.106

cāndrāyaṇaṃ vā trīn māsān abhyasyen niyatendriyaḥ
haviṣyeṇa yavāgvā vā gurutalpāpanuttaye //

Or, carrying the foot of a bedstead, dressed in (garments of) bark and allowing his beard to grow, he may, with a concentrated mind, perform during a whole year the Krikkhra (or hard, penance), revealed by Pragapati, in a lonely forest;