Shiva Purana
महापूजां महेशस्य कृत्वा मण्डलमध्यतः ॥ शिवकुंभे तथा भूयः शिवमावाह्य पूजयेत् ॥ १९ ॥
After performing great worship of Lord Mahesh in the middle of the circle In the same way, one should again invoke Lord Śiva in the Śiva-kumbha and worship him.
english translation
mahApUjAM mahezasya kRtvA maNDalamadhyataH ॥ zivakuMbhe tathA bhUyaH zivamAvAhya pUjayet ॥ 19 ॥
hk transliteration by Sanscript