Book VII · 74
No man is tired of receiving what is useful. But it is useful to act according to nature. Do not then be tired of receiving what is useful by doing it to others.
No one wearies of benefits received; and to act by the law of Nature is its own benefit. Weary not then of being benefited therein, wherein thou dost benefit others.
Marcus Aurelius, Meditations VII.74. Translated by George Long (1862). The Stoic Library.