Śāntideva said this quote

What need is there to say more?The childish work for their own benefit,The Buddhas work for the benefit of others.Just look at the difference between them.If I do not exchange my happiness, for the suffering of others, I shall not attain the state of Buddhahood.And even in Samsara I shall have no real joy. The source of all misery in the world lies in thinking of oneself;The source of all happiness lies in thinking of others.