Shiva Purana
ईश्वर उवाच ॥ स्ववामे चतुरस्रं तु मण्डलं परिकल्पयेत्॥ ओमित्यभ्यर्च्य तस्मिंस्तु शंखमस्त्रोपशोभितम्॥ १॥
Lord Śiva said:— On his left side he should arrange a four-sided circle. After worshiping him with the mantra 'Om' he placed a conch adorned with weapons.
english translation
Izvara uvAca ॥ svavAme caturasraM tu maNDalaM parikalpayet॥ omityabhyarcya tasmiMstu zaMkhamastropazobhitam॥ 1॥
hk transliteration by Sanscript