Theodore Roosevelt actually said...
Every earnest and zealous believer, every man or woman who is a doer of the word and not a hearer only, is a lifelong missionary in his or her field of labor—a missionary by precept, and, by what counts a thousand fold more than precept, by practice.
Context
Remarks at the Centennial Meeting of the Board of Home Missions of the Presbyterian Church at Carnegie Hall in New York City
05/19/1902