Class on Karma Yoga. New York, 1896. Complete Works, 1:116.

Every good work that we do without any ulterior motive, instead of
forging a new chain, will break one of the links in the existing
chains. Every good thought that we send to the world without thinking
of any return, will be stored up there and break one link in the
chain, and make us purer and purer, until we become the purest of
mortals.

Class on Karma Yoga. New York, 1896. Complete Works, 1:116.