Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 5

Sanskrit:

गत्वोदीचीं दिशं राजा रुद्रानुचरसेविताम् । ददर्श हिमवद्‌द्रोण्यां पुरीं गुह्यकसङ्कुलाम् ॥ ५ ॥

ITRANS:

gatvodīcīṁ diśaṁ rājārudrānucara-sevitāmdadarśa himavad-droṇyāṁpurīṁ guhyaka-saṅkulām

Translation:

Dhruva Mahārāja went to the northern direction of the Himālayan range. In a valley he saw a city full of ghostly persons who were followers of Lord Śiva.

Purport:

In this verse it is stated that the Yakṣas are more or less devotees of Lord Śiva. By this indication the Yakṣas may be taken to be the Himālayan tribes like the Tibetans.