From the Ramcharitamanas of Tulsidas

This and this alone
Is true religion-
To serve Thy brethren:
This is sin above all other sin,
To harm Thy brethren:
In such a faith is happiness,
In lack of it is misery and pain:
Blessed is he who swerveth not aside
From this straight path:
Blessed is he whose life is lived
Thus ceaselessly in serving God:
By bearing others' burdens,
And so alone,
Is life, true life, to be attained:
Nothing is hard to him who, casting self aside,
Thinks only this-
How may I serve fellow-men?

Source: Gandhi-The Writer, by Bhabani Bhattacharya