The story of the two birds Dharma and Adharma,
From the Saṅghabhedavastu
In the past, o monks, two Jīvajīva birds in one body, lived by the sea-shore: ‘Dharma’ and ‘Adharma’.
Once, Adharma fell asleep; Dharma was awake. He saw an ambrosia-fruit being brought by sea. He took it. He reflected: ‘What then? Shall I wake him up? Or shall I just eat this?’ He reflected further: ‘I will just eat this: it will be digested in one and the same body.’ He did not wake the other one up. He himself ate the fruit. The other one woke up. In that very place, a burp of ambrosia fruit came out from Dharma. Adharma smelt that burp. He said: ‘This is a burp...of what?’ He said: ‘It is a burp of ambrosia-fruit.’ ‘Where did you get it?’ He said: ‘I got the ambrosia-fruit while you were asleep. So, I ate it. I did not wake you up, thinking: it will be digested in one and the same body.’ The other said: ‘What you did isn’t nice! I will also find an opportunity!’
Then, on another occasion, Dharma fell asleep. Adharma was awake. He saw a poisonous fruit being brought by the sea. He ate it. Both of them fainted. Adharma, agitated due to the poisonous fruit, said: ‘In each and every one of the lifetimes that I shall be reborn, may I be the one who destroys you, your opponent, your enemy!’ Dharma said: ‘And I, also, in each and every one of the lifetimes that I shall be reborn, may I offer you my friendliness.’
The Bhagavat said: what do you think, monks? That ‘Dharma’ was none other than me, at that time, on that occasion; that ‘Adharma’ was this very Devadatta, at that time, on that occasion; there, he became irked at me for the very first time; and I remained with a friendly mind towards him.