Kaushitakagrihyasutra 5.3.29

5.3.29

ācāryasya ca mātāpitrorvapitvā tīrthaṃ gatvā tasya paścāt tiryak trīnunmṛjjya teṣvaśmano nidhāya palāśaśākhe granthiṃ kṛtvā tayoradho 'tikrāmanti \29\

And after the [death] of the teacher or the father and mother, having shaved, having gone to a bathing place, having wiped up three [heaps of earth] across behind it, having placed stones on them, and having tied a knot in two palāśa branches, they step under them.