Shiva Purana
एकाहं वा नवाहं वा तथा मंडलमेव वा । यथायोग्यं प्रकुर्वीत कालदेशानुसारतः ११६ ।
One should perform the ritual for one day, or for nine days, or even for a specific number of days according to the needs. The arrangement should be done according to time and place.
english translation
ekAhaM vA navAhaM vA tathA maMDalameva vA । yathAyogyaM prakurvIta kAladezAnusArataH 116 ।
hk transliteration by Sanscript