Śūraṅgama Sūtra
According to Hsuan Hua, the most popular example of esoteric teachings still practiced in many Chan monasteries of East Asia is the "Śūraṅgama Sūtra" and its dhāraṇī, the Śūraṅgama Mantra, along with the Nīlakaṇṭha Dhāraṇī.