Vyasasmriti 3.70

3.70

apratyaguttaraśirāḥ śayīta śayane śubhe
śaktimānucite kāle snānaṃ sandhyāṃ na hāpayet

he should lie down on a proper bed, without his head toward the west or the north. / A capable man should not neglect bathing and twilight devotion at the proper time;