Agniveshyagrihyasutra 3.6.2.6

3.6.2.6

mātari pitaryācārya iti trirātraṃ kṣāralavaṇavarjitabhojanamadhaḥśayanaṃ brahmacaryaṃ tryahaṃ ṣaḍahaṃ dvādaśāhaṃ saṃvatsaraṃ yāvadgrahaṇaṃ dvādaśāhāparārdham paramaguruṣvevamaghodakam itareṣu trirātram yāvajjīvaṃ pretapatnī \

Upon [the death of] a mother, father, or teacher, there is food free from alkaline and salt, sleeping on the ground, and chastity for three nights; for three days, six days, twelve days, a year, as long as it takes to acquire [learning], or up to twelve days; in the case of foremost elders, there is water libation for the dead thus; in the case of others, for three nights; for as long as she lives in the case of the deceased's wife.