As I discuss in this question, by far the most popular school of Hindu philosophy is the Vedanta school. But there are five other Astika or orthodox schools of Hindu philosophy: Purva Mimamsa, Samkhya, Yoga, Vaisheshika, and Nyaya. My question is about the Samkhya school, founded by the sage Kapila. Verse 55 of Ishwara Krishna's Samkhya Karika, one of the defining texts of the Samkhya school, describes the misery the soul experiences as long as it's in Samsara:
tatra jarāmaraṇakṛtaṃ duḥkham prāpnoti cetanaḥ puruṣaḥ |
liṅgasya ā vinivṛttes tasmād duḥkhaṃ svabhāvena ||
There, the intelligent Spirit experiences pain due to old age and death, till the cessation of the Linga; hence misery is of the nature of things.
Now this excerpt from the Yuktidipika, an ancient commentary on the Samkhya Karika of unknown authorship, responds to the objection that this statement does not apply to the Devas, because they aren't subject to old age:
No, because of the statement of the Smriti. Old age is that which meets decay, thus it conveys decay. That takes place in the place of gods also. Why? Because it is stated: In case of the beings falling from the world of gods there takes place close clinging to Rajas, deformity in the limbs of the body, and their blooming becomes fade. There was, the decay of the body of Shakra, etc. due to the fact of mention of the disease with reference to them. It is stated: It is the Tvashtriyam chant. It is not that Indra though toiling hard could not make all the beings sleep, he made them all sleep with this chant.
I'm interested in the part in bold. My question is, what is the story of Indra putting everyone to sleep using the Tvashtriyam chant? And how does this story demonstrate that the bodies of Devas are subject to decay?
I've never heard of the Tvashtriyam chant before, but it's presumably named after Tvashtri, which is another name for the divine architect Vishwakarma. It may be related to the story described in this chapter of the Shatapatha Brahmana of the Yajur Veda, which describes an occasion where Indra's body was weakened after drinking Soma stolen from Vishwakarma:
Now Tvashtri had a three-headed, six-eyed son. He had three mouths; and because he was thus shapen, he was called Visvarûpa ('All-shape'). One of his mouths was Soma-drinking, one spirit-drinking, and one for other food. Indra hated him, and cut off those heads of his.... Tvashtri was furious: 'Has he really slain my son?' He brought Soma juice withheld from Indra; and as that Soma-juice was, when produced, even so it remained withheld from Indra. Indra thought within himself: 'There now, they are excluding me from Soma!' and even uninvited he consumed what pure (Soma) there was in the tub, as the stronger (would consume the food) of the weaker. But it hurt him: it flowed in all directions from (the openings of) his vital airs; only from his mouth it did not flow.... Being thus purged by Soma, he walked about as one tottering. The Asvins cured him by this (offering), and caused him to be supplied with everything, for Soma is everything. By offering he indeed became better. The gods spake, 'Aha! these two have saved him, the well-saved (sutrâta):' hence the name Sautrâmanî.
This story would certainly illustrate the bodies of Devas being subject to decay. But this passage doesn't mention either the Tvashtriyam chant or Indra putting everyone to sleep, so it may not be related. In any case, does anyone know what scripture the Yukti Dipika is quoting?