SB 8.7.43
tasyapi darsayam asa
sva-viryam jala-kalmasah
yac cakara gale nilam
tac ca sadhor vibhusanam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As if in defamation, the poison born from the Ocean of Milk manifested its potency by marking Lord Siva’s neck with a bluish line. That line, however, is now accepted as an ornament of the Lord.