Shiva Purana
कृतेध्यानाज्ज्ञानसिद्धिस्त्रेतायां तपसा तथा । द्वापरे यजनाज्ज्ञानं प्रतिमापूजया कलौ ५५ ।
In the Kṛta age knowledge was acquired through meditation; in the Tretā through penance; in the Dvāpara through sacrifice and now in the Kali age it is through the worship of idols.
english translation
kRtedhyAnAjjJAnasiddhistretAyAM tapasA tathA । dvApare yajanAjjJAnaM pratimApUjayA kalau 55 ।
hk transliteration by Sanscript