Patanjali Yog Sutra
तस्य हेतुरविद्या॥२-२४॥
The reason of that (union of Purusha and Prakriti) is Avidya (ignorance).
english translation
उस प्रकृत्ति व पुरुष के संयोग का कारण वह अविद्या ही है ।
hindi translation
tasya heturavidyA॥2-24॥
hk transliteration by Sanscript