Shiva Purana
लंबयित्वा तु तत्सूत्रं सुषुम्णां तत्र योजयेत् ॥ शांतया मुद्रयादाय मूलमंत्रेण मंत्रवित् ॥ २४ ॥
After hanging the thread, one should attach it to the Suṣumna. The mantra-wise person should take the seal in peace and chant the basic mantra.
english translation
laMbayitvA tu tatsUtraM suSumNAM tatra yojayet ॥ zAMtayA mudrayAdAya mUlamaMtreNa maMtravit ॥ 24 ॥
hk transliteration by Sanscript