Shiva Purana
अहतास्तरणास्तीर्णे स दर्भशयने शुचिः ॥ मंत्रिते ऽन्तः शिवं ध्यायञ्शयीत प्राक्छिरा निशि ॥ ४२ ॥
During the night the disciple shall lie on a Darbha mattress covered with an unwashed bed-sheet and consecrated with mantra. While lying he shall meditate on Śiva and keep his head to the east.
english translation
ahatAstaraNAstIrNe sa darbhazayane zuciH ॥ maMtrite 'ntaH zivaM dhyAyaJzayIta prAkchirA nizi ॥ 42 ॥
hk transliteration by Sanscript