Bṛhadāraṇyaka Upaniṣad ("Great Forest Teaching") 5.2

5.2.1

iti vyajñāsiṣmeti hocurdāmyateti na ātthetyomiti hovāca vyajñāsiṣṭeti

The threefold descendants of Pragâpati, gods, men, and Asuras (evil spirits), dwelt as; Brahmakârins (students) with their father Pragâpati. Having finished their studentship the gods said: 'Tell us (something), Sir.' He told them the syllable Da. Then he said: 'Did you understand?' They said: 'We did understand. You told us "Dâmyata," Be subdued.' 'Yes,' he said, 'you have understood.'

5.2.3

atha hainaṃ manuṣyā ūcurbravītu no bhavāniti tebhyo haitadevākṣaramuvāca da iti vyajñāsiṣṭā

Then the men said to him: 'Tell us something, Sir.' He told them the same syllable Da. Then he said: 'Did you understand?' They said: 'We did understand. You told us, "Datta," Give.' 'Yes,' he said, 'you have understood.'

5.2.2

iti vyajñāsiṣmeti hocurdatteti na ātthetyomiti hovāca vyajñāsiṣṭeti

Then the men said to him: 'Tell us something, Sir.' He told them the same syllable Da. Then he said: 'Did you understand?' They said: 'We did understand. You told us, "Datta," Give.' 'Yes,' he said, 'you have understood.'

5.2.3-2

atha hainamasurā ūcurbravītu no bhavāniti tebhyo haitadevākṣaramuvāca da iti vyajñāsiṣṭā

Then the Asuras said to him: 'Tell us something, Sir.' He told them the same syllable Da. Then he said: 'Did you understand?' They said: 'We did understand. You told us, "Dayadham," Be merciful.' 'Yes,' he said, 'you have understood.'
The divine voice of thunder repeats the same, Da Da Da, that is, Be subdued, Give, Be merciful. Therefore let that triad be taught, Subduing, Giving, and Mercy.

5.2.3-3

iti vyajñāsiṣmeti hocurdayadhvamiti na ātthetyomiti hovāca vyajñāsiṣṭeti tadetadevaiṣādaivī vāganuvadati stanayitnurda da da iti dāmyata datta dayadhvamiti tadetattrayam̐ śikṣeddamaṃ dānaṃ dayāmiti

5.2.3-3.p1

iti pañcamādhyāye dvitīyaṃ brāhmaṇam