Mahabharata 12.259.34

अथ प्रथमकल्पेन सत्यवन्संकरो भवेत्आयुः शक्तिं च कालं च निर्दिश्य तप आदिशेत्

atha prathamakalpena satyavansaṃkaro bhavetāyuḥ śaktiṃ ca kālaṃ ca nirdiśya tapa ādiśet

Our plain-language meaning of this verse is waiting for scholar review.