Brihadaranyaka Upanishad 4.83

अथ वंशो भवति — प्रजापतेर्हृदयं यथा अभ्यतपत्तस्य तेजो रसो अजायत तदेतदृचा अभ्युक्तम् ॥

atha vamsho bhavati — prajapater hridayam yathaa abhyatapat tasya tejo raso ajaayata tad etad richaa abhyuktam

Now begins the line of teachers: Prajapati's heart was heated with meditation. From it arose the essence of light. This has been declared in the Rik verse.

अब वंश (परम्परा) — प्रजापति का हृदय जब तप से तप्त हुआ, तब उसका तेज-रस उत्पन्न हुआ। यह ऋचा-वचन से अभिहित है।