Bodhicaryavatara 1.43

1.43

nanu bhagavatāmapi maitrībalādijātakeṣu [jātakamālā-8] mahadduṣkaraṃ śrūyate / tat kathaṃ sukhenaiva sukhaṃ pravṛddhamiti? naiṣa doṣaḥ / yataḥ utpādyameva parahitasukhādhāyakaṃ duḥkhaṃ svaparayoḥ / kṛpātmabhiḥ / sukhameva tādṛśaṃ duḥkhaṃ paraduḥkhaduḥkhināṃ dhimatāmiti pratipādayiṣyate //

Objection: But even for the Blessed One, great austerities are heard of in the Maitrībala and other Jātakas; how then has happiness increased only through happiness? There is no fault here. For that suffering which brings about the welfare and happiness of others is indeed to be produced for oneself and others by those whose nature is compassion. That such suffering is nothing but joy for the wise who suffer with the suffering of others will be demonstrated later.