Matsya Purana — Pṛthu
विषं क्षीरं ततो दोग्धा धृतराष्ट्रो ऽभवत्पुनः असुरैरपि दुग्धेयम् आयसे शक्रपीडिनीम् //
viṣaṃ kṣīraṃ tato dogdhā dhṛtarāṣṭro 'bhavatpunaḥ asurairapi dugdheyam āyase śakrapīḍinīm //
Then poison and milk were drawn forth. Thereafter, Dhṛtarāṣṭra again became the agent of milking (the churning-calf). Even by the Asuras it was milked—into an iron vessel—(that substance) which torments Śakra (Indra).
It presents a cosmological “extraction” motif—poison and milk arise from a primordial churning—showing how destructive and nourishing substances emerge together in creation cycles that Purāṇas often link to Pralaya-and-renewal symbolism.
Indirectly, it teaches discernment: from the same process come both poison and milk, implying that rulers and householders must recognize and manage harmful outcomes while preserving and distributing what sustains society.
The explicit detail is ritual-technical: the substance is “milked into an iron vessel” (āyasa), reflecting Purāṇic attention to prescribed materials (metal/utensils) used in rites and handling potent substances.