Quotations about:
    heretic

These [social questions] have all been kept alive in the cauldron of our agitation, and earned us properly, deservedly, the title of “infidel” and “traitor.” “Infidel” to a church that could be at peace in the presence of sin! “Traitor” to a state that was a magnificent conspiracy against justice.

Wendell Phillips (1811–1884) American abolitionist, orator, social activist

Speech (1857-01-02), 25th Anniversary of the Massachusetts Anti-Slavery Society, Faneuil Hall, Boston
    (Source)

As recorded in The Liberator, Vol. 27, No. 2 (1857-01-09), and the National Anti-Slavery Standard, Vol. 17, No. 35 (1857-01-17).

This is the closest to primary source for a variation of a quote more commonly cited to Phillips:

Write on my gravestone: "Infidel, Traitor" -- infidel to every church that compromises with wrong; traitor to every government that oppresses the people.”

The earliest I can find this version of the quote in print is in the late 1920s (1927, 1927, 1929) in various Labor / Socialist publications, standing alone as column filler without citation.

Prior to this, I can find examples of a form closer to the one given above:

When I die I wish but two words written on my tombstone -- "Infidel" -- "Traitor." Infidel to a church that can be at peace in the presence of sin; Traitor to a government that is a magnificent conspiracy against justice.

The earliest I find this version is in Oliver Johnson, William Lloyd Garrison and His Time (1879), a quotation from Johnson of a (the same?) speech at Faneuil Hall. It's also mentioned, in whole or in part in:

• The Cube (1897-05), mentioned as a quotation from Phillips.
• The Advocate of Peace, Vol. 60, No. 9 (1898-10), printing a pacifism speech by William Lloyd Garrison (1898-08-25).
• The Labour Annual (1899), as column filler.

While it is possible that Phillips used variations of the same quotation on different occasions (as many orators and lecturers of that time and this do), the clustering of dates with versions suggests to me failures of memory (e.g., Johnson), or intentional tweakings of the text (in the 1920s) to prefer more contemporary language or political usage.

Rufus King Noyes (comp.), Views of Religion (1908), is a list of quotations about (and generally critical of) religion, in the format of giving the name, and then the quotation after this. It includes, attributed in this fashion to Phillips:

When I die, I wish but two words written on my tombstone -- "Infidel" and "Traitor."
 

The next quotation -- with its name immediately below the above, is from William Dean Howells. I did find misattributions to this and the longer quote made to Howells, probably from a misreading of this book's format.

As a final note, Phillips' gravestone did not end up including either of those words.