Shiva Purana
चतुर्ष्वपि बलिष्ठं हि शिवरात्रिव्रतं हरे॥ तस्मात्तदेव कर्तव्यं भुक्तिमुक्तिफलेप्सुभिः॥ २०॥
O Viṣṇu, among the four the most powerful is the rite of Śivarātri. Hence that alone shall be performed by those who desire the fruits of worldly pleasures and salvation.
english translation
caturSvapi baliSThaM hi zivarAtrivrataM hare॥ tasmAttadeva kartavyaM bhuktimuktiphalepsubhiH॥ 20॥
hk transliteration by Sanscript