Paraskaragrihyasutra 1.8.21

1.8.21

trirātramakṣārālavaṇāśinau syātāmadhaḥ śayīyātāṃ saṃvatsaraṃ na mithunamupeyātāṃ dvādaśarātraṃ ṣaḍrātraṃ trirātramantataḥ \21\ \\8\\

Through a period of three nights they shall eat no saline food; they shall sleep on the ground; through one year they shall refrain from conjugal intercourse, or through a period of twelve nights, or of six nights, or at least of three nights.