Devadatta as a Snake in a Previous Life

From Nagarjuna's Treatise on the Great Perfection of Wisdom
(Dharmamitra Translation)

On account of causes and conditions such as these which are associated with being poor and destitute one courses along the path of the ten unwholesome deeds. If one practices giving, then when one is born one possesses valuable goods. Because one has valuable goods one does not engage in that which is not Dharma. Why is this the case? It is because the five objects of the senses are abundant and there is nothing which one lacks."

[This principal] is illustrated by the case of Devadatta in a previous life when he was a snake who dwelt together with a frog and a turtle in a pond. They had all become close friends. Later, the water of the pond dried up. They were hungry, poor, in desperate straits and lacking in any other resources. At that time the snake dispatched the turtle to call forth the frog. The frog then sent back the turtle by uttering a verse:

If one encounters poverty and destitution one loses one's original mind.
One doesn't consider one's original principals for eating has become foremost.
You take what I tell you and so inform the snake
That this frog will never come and arrive at your side.
If, however, one cultivates giving, in later lives one will possess merit and have nothing which one lacks. If this is the case then one will be able to uphold the precepts and will be free of these manifold ills.