Vinatha and Kadru were the wives of Sage Kashyap. Kadru, with the help of her sons, who were snakes, tricked Vinatha and defeated her in a bet.
As a result, Vinatha and her son Garuda became Kadru’s slaves. The snakes told Garuda that he and his mother would be released from bondage only if Garuda brought nectar from the world of the celestials.
The nectar was closely guarded, and the snakes assumed Garuda would not be able to bring it. But he overcame all obstacles and successfully brought the nectar, said V.S. Karunakarachariar, in a discourse.
However, if the nectar were to be consumed by the snakes, it would ensure their immortality. This was not desirable for, the snakes were deceitful and wicked.
And yet, Garuda could not secure his release or his mother’s without giving the nectar to the snakes. So Garuda resorted to trickery. All that the snakes had told him was that he should bring the nectar.
They had not laid down the condition that he should enable them to consume it.
So Garuda told the snakes that they should first have a bath and perform some rituals, before they could have the nectar.
While the snakes were away, Indra came down and retrieved the nectar and took it away to the celestial world. Garuda had only promised to fetch the nectar. He had not promised to prevent Indra from retrieving it. So Garuda was not really breaking any promise. He had kept his word and brought the nectar.
Garuda was perfectly justified in tricking the snakes for, after all that was what they had done to his mother!