Verse 1.5.4

एतमु एवाहमभ्यगासिषं तस्मान्मम त्वमेकोऽसीति ह कौषीतकिः पुत्रमुवाच प्राणांस्त्वं भूमानमभिगायताद्बहवो वै मे भविष्यन्तीति ॥ १.५.४ ॥

etamu evāhamabhyagāsiṣaṃ tasmānmama tvameko'sīti ha kauṣītakiḥ putramuvāca prāṇāṃstvaṃ bhūmānamabhigāyatādbahavo vai me bhaviṣyantīti || 1.5.4 ||

4. The sage Kauṣītaki said to his son: ‘I worshipped prāṇa as just one entity, and therefore I had only one son. I suggest that you worship prāṇa as one with manifold qualities and with many forms while thinking, “May my children be many”’.

Word-for-word explanation:

Kauṣītakiḥ ha putram uvāca, Kauṣītaki said to his son; aham u etam eva abhyagāsiṣam, I worshipped this [prāṇa] as one; tasmāt, that is why; tvam mama ekaḥ, you are my only son; tvam prāṇān bhūmānam abhigāyatāt, you should worship prāṇa as many [i.e., with manifold qualities and forms]; me bahavaḥ vai bhaviṣyanti iti, thinking, ‘May my children be many.’

Commentary:

The sun and its rays are not separate, but if a person wants more than one child, he or she will have to worship the sun and its rays as separate entities. The same applies to the worship of the chief prāṇa and its subsidiaries (vyāna, udāna, etc.).