Shiva Purana
रौद्रकादशकाख्यं यत्कैलासं षट्सहस्रकम् ॥ शतरुद्रं त्रिसाहस्रं कोटिरुद्रं ततः परम् ॥ ५४ ॥
There are six thousand mountains known as Raudrakādaśaka. One hundred Rudras, three thousand Rudras and one crore Rudras beyond that.
english translation
raudrakAdazakAkhyaM yatkailAsaM SaTsahasrakam ॥ zatarudraM trisAhasraM koTirudraM tataH param ॥ 54 ॥
hk transliteration by Sanscript