Shankhayanagrihyasutra 2.2.2

2.2.2

: iyam duruktāt paribādhamānā varṇam pavitram punatī na āgāt.|.prāṇa apānābhyām balam āviśantī sakhā devī subhagā mekhalā iyam iti.|.trir mekhalām pradakṣiṇam triḥ pariveṣṭya.

(There should be) one knot, or also three, or also five.